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1
MATHEMATICS–12
ANSWERS TO MOCK TEST PAPER 1. (a) 2. (c) 3. (c) 4. (b) 5. (b) 6. (d) 7. (a) 8. (b) 9. (c) 10. (d) 11. x + y – z = 2
12. ( ) ( )ˆ ˆˆ ˆ ˆ ˆ5 4 6 3 7 2r i j k i j k= − + + λ + + 13. (–1, 1) 14. –f (x) 15. 1 16. If A and B are skew-symmetric matrices, then A + B also skew-symmetric. Let A and B be two skew-symmetric matrices of the same order. Then, A′=–A and B′=–B Now (A+B)′=A′+B′=–A–B=–(A+B) ⇒ A + B is a skew-symmetric matrix. 17. sin2a + sin2b + sin2g = 1 – cos2a + 1 – cos2b + 1 – cos2g = 3 – (cos2a + cos2b + cos2g) = 3 – 1 = 2 [ cos2a + cos2b + cos2g = 1]
18. I = 3 2 2− −⋅∫ x xe dxI II
On Integrating by parts, we get
I = 3 3 3 22 2 2 2− − − −∫ ∫∫− −( )
x x x xe dx e dx dxlog
= 32
3 3 22
22
22
−−
−−
−
− −( )
−( )∫xx
xxe e dxlog
= 32
3 322
2 2−−
− −
−
− ⋅∫xx
x xe e dxlog = 32
322
−−
−
− ⋅xxe log I
I + log3 · I = 3
2
2 2− −⋅−
x xe
(1 + log3) I = 3
2
2 2− −⋅−
x xe
I = 32 1 3
2 2− −⋅− +( )
x xelog =
−( )+( )
−32 1 3
2e x
log
19. f (x) = x2 4− , a = 2, b = 4 Q f (x)hasuniqueanddefinitevalueforeachxintheclosedinterval[2,4]. \ f (x) is continuous in [2, 4].
f ′(x) = 12
4 221
2x x−( ) ×−
= x
x2 4−
which exists for all xintheopeninterval]2,4[ i.e., for 2 < x < 4], f (x)isderivablein]2,4[
1st Proof \ Anjum Azad \ Mock_ans_(Mathe-12) \ 30-01-20\17:36 Reader _______________________ Date __________
2 n MatheMatics – Xii
1st Proof \ Anjum Azad \ Mock_ans_(Mathe-12) \ 30-01-20\17:36 Reader _______________________ Date __________
\ByLagrange’sMeanValueTheorem,wehave
f ′(c) = f b f ab a
f f( ) − ( )−
= ( ) − ( )−
4 24 2
c
c2 4− =
12 02
2 32
3− = = i.e., ⇒ c2 = 3(c2 – 4) ⇒ 2c2 = 12, \ c2 = 6 ⇒ c = ± 6 Rejecting c = – 6 which does not lie in ]2, 4[ \ c = 6 , which lies in ]2, 4[ Hence,theLMVTheoremisverified.
OR
f (x) = x −( )823
f (x) is continuous in [0, 16]
f ′ (x) = 23
813x −( )− =
2
3 813x −( )
Which does not exist at x = 8 Œ[0, 16] So, f (x)isnotderivablein(0,16).Hence,Rolle’stheoremisnotapplicable.
20. f (x) = x
xsin
\ f ′ (x) = sin cos
sinx x x
x1
2
( ) − ⋅( )
⇒ f ′ (x) = cos tan
sinx x x
x−( )
2 ...(i)
Now, cos x > 0 for 0 < x < π2
and sin x < x < tan x for 0 < x < π2
Q lim sinx
xx→
=
0
1
\ (tan x – x) > 0
\ From (i),wehavef ′(x) > 0 for 0 < x < π2
Thus, f (x)isanincreasingfunctionintheinterval0<x < π2
. 21. y = x2 + 2x + 3
dydx
= 2x + 2
dydx
( )at 0 3,
= 2(0) + 2 = 2
y – y1 = dydx x y
( )at 1 1,
(x – x1)
y – 3 = 2 (x – 0) ⇒ 2x – y + 3 = 0
answers to Mock test paper n 3
1st Proof \ Anjum Azad \ Mock_ans_(Mathe-12) \ 30-01-20\17:36 Reader _______________________ Date __________
22. The equation of the lines are
xyp
z−−
=−( ) = −1
37 2
23
2 and
7 13
51
65
xp
y z−( )−
= − = −−
⇒ x y
pz−
−= − = −1
32
27
32
and xp
y z−− = − = −
−1
37
51
65
Since the lines are at right angle, therefore, a1a2 + b1b2 + c1c2 = 0
⇒ (–3) −
+
37
27
p p (1) + (2)(–5) = 0
⇒ 97
27
p p+ – 10 = 0 ⇒ 117p = 10 ⇒ p = 70
11OR
− +−
= − = +−
x y z22
17
33
and x y z+−
= − = −21
2 84
54
⇒ x y z− = − =
− −( )−
22
17
33
and x y z− −( )
−= − = −2
14
25
4 \ a1 = 2, b1 = 7, c1 = –3 and a2 = –1, b2 = 2, c2 = 4
cos q = a a b b c c
a b c a b c1 2 1 2 1 2
12
12
12
22
22
22
+ +
+ + + +
= 2 1 7 2 3 4
2 7 3 1 2 42 2 2 2 2 2
−( ) + ( ) + −( )( ) + ( ) + −( ) −( ) + ( ) + ( )
= − + −2 14 12
62 21 = 0
cos q = 0 ⇒ q = π2
23. limx
f x→ −
( )5
= limx
kx→ −
+( )5
1 = limh
k h→
−( ) + 05 1 = k(5 – 0) + 1 = 5k + 1
limx
f x→ +
( )5
= limx
x→ +
−( )5
3 5 = limh
h→
+( )03 5 –5 = 3(5 + 0) – 5 = 15 – 5 = 10
As f (x) is continuous at x = 5, So, limx
f x→ −
( )5
= limx
f x→ +
( )5
⇒ 5k + 1 = 10 ⇒ k = 95
24. Let 12
tan–1x = q
tan–1x = 2 q ⇒ x = tan 2 q ...(i)
R.H.S. = cos tantan
− + ++
12
2
1 1 22 1 2
θθ
= cos secsec
− +
1 1 2
2 2θ
θ
= cos cos− +
1 1 2
2θ
= cos cos−
122
2θ
= cos–1 cos q = q = 12
tan–1x [using (i)]
4 n MatheMatics – Xii
1st Proof \ Anjum Azad \ Mock_ans_(Mathe-12) \ 30-01-20\17:36 Reader _______________________ Date __________
OR
Wehave 9 − −π8
94
13
1sin = 94
2 23
1sin−
⇒ 94
2 23
13
1 1sin sin− −+
=
98π
Now, L.H.S. = 94
2 23
13
1 1sin sin− −+
= 94
2 23
1 13
13
1 2 23
12 2
sin− −
+ −
[Q sin–1 x + sin –1 y = sin–1 ( )x y y x1 12 2− + − ]
= 94
2 23
1 19
13
1 89
1sin− − + −
=
94
2 23
2 23
13
13
1sin− × + ×
= 94
89
19
1sin− +
=
94
11sin− = 94 2
× π =
98π
= R.H.S.
Hence, 98 4
13
1π − 9 −sin = 9 −
42 2
31sin
25. Given: y log ydx – xdy = 0 ⇒ y log ydx = xdy
or dyy ylog
= dxx
Integration both sides, we get
1yydy
log∫ = dxx∫ ⇒ log (log y) = log x + log c
⇒ log (log y) = log cx ⇒ loge y = cx or y = ecx is the required solution. [Q elog f (x) = f (x)]
26. I = log tan xdx02π
∫ = log tan ππ
202 −
∫ x dx Q f x dx f a x dx
a a( ) = −( )
∫ ∫0 0
= logcot log tanxdx x dx02 1
02
π π
∫ ∫= ( )−
= −∫ log tan xdx02π
= –I ⇒ 2I = 0 or I = 0
27. D = b c c a a bc a a b b ca b b c c a
+ + ++ + ++ + +
= 0
answers to Mock test paper n 5
1st Proof \ Anjum Azad \ Mock_ans_(Mathe-12) \ 30-01-20\17:36 Reader _______________________ Date __________
Applying C1 ÆC1 + C2 + C3
D = 222
a b c c a a ba b c a b b ca b c b c c a
+ +( ) + ++ +( ) + ++ +( ) + +
= 0
⇒ D = 2111
a b cc a a ba b b cb c c a
+ +( )+ ++ ++ +
= 0
Applying R2 ÆR2 – R1 and R3 ÆR3 – R1
⇒ D = 2100
a b cc a a bb c c ab a c b
+ +( )+ +− −− −
= 0
⇒ D = 2(a + b + c)[1·(b – c)(c – b) – (b – a)(c – a)] = 0 D = 2(a + b + c)[ab + bc +ca – (a2 + b2 + c2)] = 0 D = –(a + b + c)[–2(ab + bc +ca) +2(a2 + b2 + c2)] = 0 D = –(a + b + c)[(a – b)2 + (b – c)2 + (c – a)2 = 0 ⇒ (a + b + c) = 0 or (a – b)2 + (b – c)2 + (c – a)2 = 0 ⇒ a + b + c = 0 or a = b = c
OR
D = p b ca q ca b r
= 0
Applying R1 ÆR1 – R2 and R2 ÆR2 – R3
D = p a b q
q b c ra b r
− −− −
00 = 0 ⇒ D =
p a q bq b r c
a b r
− − −( )− − −( )
00 = 0
Expanding along C1, we get D = (p – a) [(q – b)r +(r – c)b] + a[(q – b)(r – c) – 0] = 0 As a ≠ p, b ≠ q, c ≠ r,dividingthroughoutby(p – a) (q – b) (r – c), we get
rr c
bq b
ap a−
+−
+−
= 0
Adding 2 to both sides, we get
rr c
bq b
ap a−
+−
+
+−
+
1 1 = 1 + 1 ⇒ rr c
b q bq b
a p ap a−
+ + −−
+ + −−
= 2
⇒ rr c
qq b
pp a−
+−
+−
= 2
28. y = sin− − − −
1 21 1x x x x
Put x = sin q and x = sin f, we get
\ y = sin sin sin sin sin− − − −
1 2 21 1θ φ φ θ
6 n MatheMatics – Xii
1st Proof \ Anjum Azad \ Mock_ans_(Mathe-12) \ 30-01-20\17:36 Reader _______________________ Date __________
\ y = sin sin cos sin cos− −
1 2 2θ φ φ θ
⇒ y = sin–1 [sin q cos f – sin f cos q] ⇒ y = sin–1 [sin (q – f )] = q – f \ y = sin–1 x – sin–1 x
⇒ dydx
= 1
11
11
22−−
−⋅
x x x
Hence, dydx
= 1
11
22 2−−
−x x x 29.Tofindthepointofintersectionofthecurves y2 = 4x ...(i) and 4x2 + 4y2 = 9 ...(ii) Weequatevaluesofy2 from these equations.
4x = 94
– x2 ⇒ x2 + 4x – 94
= 0
⇒ 4x2 + 16x – 9 = 0 ⇒ 4x2 + 18x – 2x – 9 = 0 ⇒ 2x(2x + 9) – 1(2x + 9) = 0 ⇒ (2x – 1) (2x + 9) = 0
⇒ x = 12
and x = – 92
which is rejected because if x = – 92
, then from the equation of the
parabola
y2 = 4 92
−
= –18 < 0 which is not possible.
Hence, x ≠ – 92
\ x = 12
When, x = 12
, y2 = 4 × 12
= 2 ⇒ y = ± 2
\ The points of intersection are B 12
2,
and C 12
2,−
Required area = Area of the region OCABO
= 2(Area of the region OMABO) [By symmetry]
= 2[(Area of the region OMBO) + (Area of the region BMAB)]
= 2 2 940
1 22
1 2
3 2
xdx x dx/
/
/
∫ ∫+ −
Y
Y′
X′
X
O
M
C
B
A
1
22,( (
1
22,−( (
3
20,( (
y
x2 =
4
4 + 4x2
y2
= 9
answers to Mock test paper n 7
1st Proof \ Anjum Azad \ Mock_ans_(Mathe-12) \ 30-01-20\17:36 Reader _______________________ Date __________
= 4 32
22
94
98 3
2
32
12
2 1
12
32
x x x x
+ − +
−sin
= 83
12
0 94
94
23
32 2
12
32
1
12
−
+ −
+
−x x xsin332
= 83
12 2
0 12
94
14
94
1 13
1 1× + − −
+ −
− −sin sin
= 43 2
94 2
13
12
21+ −
−−π sin = 98
94
13
43 2
12
1π − + −−sin
= 98
94
13
13 2
1π − +−sin = 98
94
13
26
1π − +−sin sq. units
30. Wehave, 1 1+
+ −
e dxdy
e xy
xy
xy = 0
dxdy
= e x
y
e
xy
xy
−
+
1
1 ...(i)
Which is a homogeneous equation of the form dxdy
= f xy
Put x = vy, so that dxdy
= v + y dvdy
\ The equation (i) becomes v + y dvdy
= e v
e
v
v
−( )+
11
⇒ y dvdy
= ve ee
v v
v
−+1
– v ⇒ y dvdy
= − −+e ve
v
v1
⇒ 1+
+e
v edv
v
v = – dyy
Integrating both sides, we get
1++
∫
ev e
dvv
v = – dyy∫
log (v + ev) = – log y + log C ⇒ logxyexy+
= log
Cy
8 n MatheMatics – Xii
1st Proof \ Anjum Azad \ Mock_ans_(Mathe-12) \ 30-01-20\17:36 Reader _______________________ Date __________
⇒ xyexy+ =
Cy
⇒ x yexy+ = C is the required solution.
31. We know that 2 tan–1 x = cos− −+
12
2
11
xx
LHS = 22
1tan tan− −+
α βα β
A = cos
tan
tan
−
− −+
+ −+
1
2
2
12
12
α βα βα βα β
A
A
= costan tan
tan
−
−
+ +
+ 1
2 2
2
12
12
12
α β
α
A A
A
+ −
β 12
2tan A
= coscos sin cos sin
−
−
+
+
1
2 2 2 2
2 2 2 2α βA A A A
+
+
α βcos sin cos2 2 2
2 2 2A A A
−
sin2
2A
= cos coscos
− ++
1 α βα β
AAOR
Given, cos–1 x + cos–1 y + cos–1z = p ⇒ cos–1 x + cos–1 y = p – cos–1z
⇒ cos− − − −( )1 2 21 1xy x y = p – cos–1z
⇒ xy x y− − −1 12 2 = cos (p – cos–1z)
⇒ xy x y− − −1 12 2 = – cos (cos–1z) ⇒ xy x y− − −1 12 2 = – z
⇒ xy + z = 1 12 2− −x y ⇒ (xy + z)2 = (1 – x2) (1 – y2)
⇒ x2y2 + z2 + 2xyz = 1 – x2 – y2 + x2y2
⇒ x2 + y2 + z2 + 2xyz = 1
32. When a die is thrown, sample space = {1, 2, 3, 4, 5, 6}
p = probability of throwing six when a die is thrown = 16
q = probability of throwing six = 1 – p = 1 – 16
= 56
Captain of team A can win in 1st, 3rd, 5th .... throws
answers to Mock test paper n 9
1st Proof \ Anjum Azad \ Mock_ans_(Mathe-12) \ 30-01-20\17:36 Reader _______________________ Date __________
P(A win) = 16
56
16
56
16
2 4
+
+
+ .... =
16
1 56
2
−
Sum S∞ =−
ar1
= 16
3611
611
× =
P(B win) = 1 611
511
− =
As probability of winning the match by team A and team B are not the same
P A P B( ) = 6 > ( ) =
11
511
, so decision of referee was not fair.
33. A = 1 1 23 0 21 0 3
−−
|A| = 1 1 23 0 21 0 3
−− = 9 + 2 = 11
A11 = 0, A21 = 3, A31 = 2; A12 = –11, A22 = 1, A32 = 8; A13 = 0, A23 = –1, A33 = 3
Adj A = 0 3 211 1 80 1 3
−−
A(Adj A) = 1 1 23 0 21 0 3
−−
0 3 211 1 80 1 3
−−
=
0 11 0 3 1 2 2 8 60 0 0 9 0 2 6 0 60 0 0 3 0 3 2 0 9
+ + − − − +− − + + + −+ + + − + +
= 11 0 00 11 00 0 11
= 11I = |A|I
(Adj A)A = 0 3 211 1 80 1 3
−−
1 1 23 0 21 0 3
−−
=
0 9 2 0 0 0 0 6 611 3 8 11 0 0 22 2 240 3 3 0 0 0 0 2 9
+ + + + − +− + + + + − − +
− + + + + +
= 11 0 00 11 00 0 11
= 11I = |A|I
So, A(adj A) = A (adj A) = |A|IOR
Let cost of 1 pen = ` x cost of 1 pag = ` y cost of 1 instrument box = ` z Equations are 3x + 2y + 1z = 41 2x + 1y + 2z = 29 3x + 2y + 2z = 46
10 n MatheMatics – Xii
1st Proof \ Anjum Azad \ Mock_ans_(Mathe-12) \ 30-01-20\17:36 Reader _______________________ Date __________
|A| = 3 2 12 1 23 2 2
= – 1
Let AX = B, here B = 412946
, X =
xyz
A11 = –2, A21 = –2, A31 = 3; A12 = 2, A22 = 3, A32 = –4; A13 = 1, A23 = 0, A33 = –1
A–1 = 11
2 2 32 3 41 0 1−
− −−−
X = A –1B ⇒ xyz
= 1
1
2 2 32 3 41 0 1−
− −−−
412946
⇒ xyz
=
2155
x = ` 2, y = ` 15, z = ` 5 34. Step I. Mathematical Formulation of L.P.P. Suppose the farmermixes x bags of brand P and y bags of brandQ.The given data is
condensed in the following table.Brand Number
of bagsCost
(`/bag)Element A(units/bag)
Element B(units/bag)
Element C(units/bag)
P x 250 3 2.5 2Q y 200 1.5 11.25 3
Total cost = 250x + 200y Let Z = 250x + 200y Wehavethefollowingmathematicalmodelforthegivenproblem: Minimise Z = 250x + 200y ...(i) subjecttotheconstraints: 3x + 1.5y ≥ 18 [Given: Minimum requirement of nutritional element A is 18 units i.e., ≥ 18 units]
or 3x + 1510
y ≥ 18
Multiplyingby10anddividingby15, or 2x + y ≥ 12 (Nutritional element A constraint) ...(ii) 2.5x + 11.25y ≥ 45 [Given: Minimum requirement of nutritional element B is, 45 units i.e., ≥ 45 units]
or 2510 x +
1125100
y ≥ 45
or 2x + 9y ≥ 36 (Nutritional element B constraint) ...(iii) 2x + 3y ≥ 24 (Nutritional element C constraint) ...(iv) [Given: Minimum requirement of nutritional element C is 24 units i.e., ≥ 24 units] x, y ≥ 0 (Qnumberofbagscan’tbenegative) ...(v)
answers to Mock test paper n 11
1st Proof \ Anjum Azad \ Mock_ans_(Mathe-12) \ 30-01-20\17:36 Reader _______________________ Date __________
Step II. Constraint (v) x, y ≥ 0 ⇒Feasibleregionisinfirstquadrant. Table of values for the line 2x + y = 12 of constraint (ii)
x 0 6y 12 0
Draw the straight line joining the points (0, 12) and (6, 0). Let us test for origin (x = 0, y = 0) in constraint 2x + y ≥ 12,wehave0≥ 12 which is not true. \ Region for constraint (ii) 2x + y ≥ 12 is the half-plane not containing the origin i.e., region
on the non-origin side of the line 2x + y = 12. Table of values for the line 2x + 9y = 36 for constraint (iii)
x 0 18y 4 0
Let us draw the line joining the points (0, 4) and (18, 0). Let us test for origin (x = 0, y = 0) in constraint (iii) 2x + 9y ≥ 36,wehave0≥ 36 which is not
true. \ Region for constraint (iii) is the region on the non-origin side of the line 2x + 9y = 36. Table of values for the line 2x + 3y = 24 for constraint (iv)
x 0 12y 8 0
Draw the line joining the points (0, 8) and (12, 0). Let us test for origin (x = 0, y = 0) in constraint (iii) 2x + 3y ≥ 24,wehave0≥ 24 which is not
true. \ Region for constraint (iii) 2x + 3y ≥ 24 is again the region on the non-origin side of the
line 2x + 3y = 24. Theshadedregioninthefigureisthefeasibleregiondeterminedbythesystemofconstraints
from (ii) to (v). The feasible region is unbounded. Step III.ThecoordinatesofthecornerpointsAandDare(18,0)and(0,12)respectively. Corner point B: It is the point of intersection of the lines 2x + 3y = 24 and 2x + 9y = 36
Subtracting – 6y = – 12 ⇒ y = −−126
= 2
Putting y = 2 in 2x + 3y=24,wehave 2x + 6 = 24 ⇒ 2x = 18 ⇒ x = 9 \ Corner point B is (9, 2). Corner point C: It is the point of intersection of the lines 2x + y = 12 and 2x + 3y = 24
Subtracting – 2y = – 12 ⇒ y = −−122
= 6 Putting y = 6 in 2x + y=12,wehave 2x + 6 = 12 ⇒ 2x = 6 ⇒ x = 3 \ Corner point C is (3, 6).
12 n MatheMatics – Xii
1st Proof \ Anjum Azad \ Mock_ans_(Mathe-12) \ 30-01-20\17:36 Reader _______________________ Date __________
2O 4
2
4
6
8
10
12
14
16
6 8 10 12 14 16 18 20
XX¢
Y¢
Y
D(0, 12)
C(3, 6)
B(9, 2)
A(18, 0)
2x+ 9y = 36
5x+ 4y = 39
2x+ y = 12
2x+ 3y = 24
(12, 0)(6, 0)
(0, 4)
(0, 8)
Feasible Region
Step IV.Now,weevaluateZateachcornerpoint.
Corner Point Z = 250x + 200yA(18, 0) 4500B(9, 2) 2650C(3, 6) 1950 = m ← Smallest
D(0, 12) 2400 Fromthistable,wefindthat1950isthesmallestvalueofZatthecornerC(3,6).Sincethe
feasibleregionisunbounded,1950mayormaynotbetheminimumvalueofZ. Step V. To decide this, we graph the inequality Z < m i.e., 250x + 200y < 1950 or 5x + 4y < 39. Table of values for the line 5x + 4y = 39 corresponding to constraint Z < m i.e., 5x + 4y < 39.
x 0 395
= 7.8
y 394
= 9.75 0
Let us draw the dotted line joining the points (0, 9.75) and (7.8, 0).
answers to Mock test paper n 13
1st Proof \ Anjum Azad \ Mock_ans_(Mathe-12) \ 30-01-20\17:36 Reader _______________________ Date __________
The line is to be shown dotted because equality sign is absent in the constraint Z < m i.e., in 5x + 4y < 39.
Let us test for origin (x = 0, y=0)inthisconstraint,wehave0<39whichistrue. \ Region for constraint Z < m i.e., 5x + 4y < 39 is towards the origin side of the line. WeobservethatthehalfplanedeterminedbyZ<m has no point in common with the feasible
region.Hencem=1950istheminimumvalueofZattainedatthepointC(3,6). \ Minimum cost is ` 1950 when 3 bags of brand P and 6 bags of brand Q are mixed. 35.Letrbetheradiusofthegivenrightcircularconeofgivenheighth. Let the radius of the inscribed cylinder be x and its
height be y. InsimilartrianglesAPQandARC,wehave
PQRC
= APAR
i.e., xr
= h yh−
[Q AP = AR – PR = h – y] Cross-multiplying, hx = rh – ry \ ry = rh – hx = h(r – x)
\ y = hr
(r – x)...(i)(givencondition)
Letzdenotethevolumeofthecylinder \ z = px2y ...(ii) [Here z is to be maximised] Puttingthevalueyfrom(i) in (ii),
z = px2 hr
(r – x) = πhr
(rx2 – x3) ...(iii)
\ dzdx
= πhr
(2rx – 3x2), d zdx
2
2 = πhr
(2r – 6x)
For max. or min. put dzdx
= 0
\ πhr
(2rx – 3x2) = 0 or πhr
x (2r – 3x) = 0
But x ≠ 0, \ 2r – 3x = 0 or 3x = 2r or x = 23r
At x = 23r
, d zdx
2
2 = πhr
2 123
r r−
=
πhr
(– 2r) = – 2ph whichisnegative.
\ z is maximum at x = 23r
.
Putting x = 23r
in (i), y = hr
r r−
23
= hr
·r3
= h3
Putting x = 23r
in eqn. (iii),
Maximumvolumeofcylinder=πhr
r r r⋅ −
49
827
2 2
y
x
α
A
B C
R
P Q
14 n MatheMatics – Xii
1st Proof \ Anjum Azad \ Mock_ans_(Mathe-12) \ 30-01-20\17:36 Reader _______________________ Date __________
= πhr
r3 49
827
−
= phr2 12 8
27−
= 427
phr2 = 427
ph (h tan a)2
Q In ARC RCAR
∆ , tan . ., tan tan= = ∴ =
α α αi e rh
r h
= 427
ph3tan2 a.
OR AC = 2R and BC = x Radius of the cylinder
= 12
4 2 2R − x
= V = π 12
4 2 22
R −
x x
⇒ V = π4
4 2 3R x x−( )
Find ddxVandsolve
ddxV
= 0 ⇒ x = 2
3R
Vmax = π4
4 2 3R x x−( ) = 43 3
3πR
\ Vmax = 13
43
3πR
= 13
(Volume of sphere)
36.Cartesianequationofgivenplanesare 2x + y – 3z + 4 = 0 ...(i) and 3x + 4y + 8z – 1 = 0 ...(ii) Let the equation of the required plane be (2x + y – 3z + 4) + l(3x + 4y + 8z – 1) = 0 ⇒ (2 + 3l)x + (1 + 4l)y + (–3 + 8l)z + (4 – l) = 0 ...(iii) For point A(a,0,0), equation (iii) becomes (2 + 3l)a + (4 – l) = 0 ...(iv) For point B(0,a,0), equation (iii) becomes (1 + 4l)a + (4 – l) = 0 ...(v) By equation (iv) and equation (v), we get (1 + 4l)a – (2 + 3l)a = 0 ⇒ l = 1 Put l = 1 in equation (iii), we get [2 + 3(1)]x + [1 + 4(1)]y + [–3 + 8(1)]z + 4 – 1 = 0 i.e., 5x + 5y + 5z + 3 = 0
qqq
A
CD
x2R
O
B
4R –2 2x
B
A
C
a
aa
(0, ,0)a
( ,0,0)a
(0,0, )a
X
Z
Y