- #1
vmr101
Gold Member
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Homework Statement
i)Use integration by parts to express:
I(n) = ∫ sin^n (x) dx
in terms of I(n-2).
ii) Hence show that ∫(π/2 for top, π/4 for bottom) 1/[sin^4 (x)] dx = 4/3
Homework Equations
Reduction Formula and Trig Identity [sin²(x) + cos²(x) = 1]
π = pi
The Attempt at a Solution
i) Integrate by parts with
u = sin^(n-1)(x) => du = (n-1)·cos(x)·sin^(n-2)(x)
dv = sin(x) => v = -cos(x)
I ended up with:
∫ sin^n(x) dx
= -(1/n)·cos(x)·sin^(n-1)(x) + [(n-1)/n]· ∫ sin^(n-2)(x) dx
ii) Would this be integration by substitution and parts?
= log{ -(1/4)·cos(x)·sin^(3)(x) + [3/4]· ∫ sin^(2)(x) dx }
=> log{ -(1/4)·cos(x)·sin^(3)(x) + [3/4]·(-(1/2)·cos(x)·sin(x) + [1/2]) }
I pushed the numbers through but got this wrong, where did i go wrong?
Thanks in advance.