y = 1
4x2
−1
2ln x ⇒
dy
dx=
x
2−
1
2x⇒ 1 +
(
dy
dx
)2
= 1 +x2
4−
1
2+
1
4x2=
x2
4+
1
2+
1
4x2=
(
x
2+
1
2x
)2
. So
S =∫
4
12πx
√
(
x
2+
1
2x
)2
dx = 2π∫
4
1x
(
x
2+
1
2x
)
dx = π∫
4
1(x2 + 1) dx = π
[
1
3x3 + x
]4
1
= π[(
64
3+ 4
)
−
(
1
3+ 1
)]
= 24π