Post on 18-Jan-2016
10.6 Polar Coordinates10.7 Graphs of Polar equations
Polar coordinates
• An initial ray (polar axis) from a fixed point (the pole or origin); (r, θ)
• r = directed distance from O to P
• θ = directed angle, counterclockwise from the polar axis
Graphing polar coordinates
• r is the radius of the circles that make up the graph
• θ is the directed angle from the positive x axis
• Since polar coordinates are on the unit circle there are multiple representations for one point
• (r, θ) = (r, θ+/- 2nπ)
• (r, θ) = (-r, θ+/- (2n+1)π)
• The pole is represented by (0, θ) where θ is any angle
• To convert polar to rectangular coordinates
222 tan
sin cos
yxrx
y
ryrx
Convert to rectangular coordinates
6
7,2
r = 2θ = 7π/6
6
7sin2
6
7cos2
y
x
Convert to polar coordinates (-4, 1)
4
1tan
x
y
144
1tan 1
90
7 17
17
)1()4(2
222
222
r
r
r
yxr
Equation Conversion
• To convert rectangular to polar form use x = rcosθ and y = rsinθ
• When given polar form r = c (c is a real number) the rectangular equation is a circle of radius c so x2 + y2 = r2
• When given θ=c use tan θ = y/x
• When given r = a trig function, convert the trig function to sin or cos
Graphs of Polar equations• Change MODE on calculator to POL
• Y = is now r=
• Use the table to plot points where r is the horizontal axis and θ is the vertical axis
• In the window you can set max/min for θ
• Use TRACE to find the maximum r-value
Tests for Symmetry• The line θ = π/2; replace (r, θ) by
(r, π-θ) or (-r, -θ)• The polar axis; replace (r, θ) by (r, -θ)
or (-r, π-θ)• The pole; replace (r, θ) by (r, π+θ) or
(-r, θ)
θ=π/2Polaraxis
Pole
Analyzing the curve
• Use the chart on page 750 to identify the type of curve
• Identify the type of symmetry
• Find the maximum r value
• Find the zeros of r