∫ sin² ( x ) dx
Write sin² ( x ) as:
1 / 2 - 1 / 2 cos ( 2 x)
∫ sin² ( x ) dx = ∫ 1 / 2 dx - 1 / 2 ∫ cos ( 2 x ) dx
∫ sin² ( x ) dx = 1 / 2 x - 1 / 2 ∫ cos ( 2 x ) dx
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∫ cos ( 2 x ) dx
Substitution:
u = 2 x
du = 2 dx
dx = du / 2
∫ cos ( 2 x ) dx = ∫ cos ( u ) du / 2 = 1 / 2 ∫ cos ( u ) du = 1 / 2 sin ( u ) + C
∫ cos ( 2 x ) dx = 1 / 2 sin ( 2 x ) + C
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∫ sin² ( x ) dx = 1 / 2 x - 1 / 2 [ 1 / 2 sin ( 2 x ) ] + C
∫ sin² ( x ) dx = 1 / 2 x - 1 / 4 sin ( 2 x ) + C
∫ sin² ( x ) dx = 2 / 4 x - 1 / 4 sin ( 2 x ) + C
∫ sin² ( x ) dx = [ 2 x - sin ( 2 x ) ] / 4 + C
1.
0
∫ sin² ( x ) dx = [ 2 ∙ 2 π - sin ( 2 π ) ] / 4 - [ 2 ∙ 0 - sin ( 0 ) ] / 4 =
2π
[ 4 π - 0 ] / 4 - ( 0 - 0 ) / 4 = 4 π / 4 - 0 = π
The area bounded_
0
∫ sin² ( x ) dx = π
2π
2.
The volume of the solid formed by revolving the region bounded by the curve y=f(x) and the x−axis between x = a and x = b about the x- axis is given by:
V =
b
∫ π [ f(x)² ] dx
a
In this case:
2π
∫ π [ sin( x²)² ] dx = π sin⁴ ( x ) dx
0
2π
∫ π sin⁴ ( x ) dx
0
You solve that.
∫ sin⁴ ( x ) dx = [ sin ( 4 x ) - 8 sin ( 2 x ) +12 x ] / 32 + C
V =
2π
∫ π sin⁴ ( x ) dx = 3 π² / 4
0
Given the area bounded by the curve y = 2sin^2 x and the x - axis between
x = 0 and x = pi.
Calculate:
.1 the area bounded. (4)
.2 the volume of the solid of revolution if this area rotates
around the x - axis. (6)
1 answer