积分,求帮忙
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∫(0->1) x^3. √(1-x^2) dx
let
x=sinu
dx= cosu du
x=0, u=0
x=1, u=π/2
∫(0->1) x^3. √(1-x^2) dx
= ∫(0->π/2) (sinu)^3. (cosu)^2 du
= -∫(0->π/2) (sinu)^2. (cosu)^2 d(cosu)
= -∫(0->π/2) [ 1- (cosu)^2 ]. (cosu)^2 d(cosu)
= - [(1/3)(cosu)^3 - (1/5)(cosu)^5 ]|(0->π/2)
=1/3 -1/5
=2/15
let
x=sinu
dx= cosu du
x=0, u=0
x=1, u=π/2
∫(0->1) x^3. √(1-x^2) dx
= ∫(0->π/2) (sinu)^3. (cosu)^2 du
= -∫(0->π/2) (sinu)^2. (cosu)^2 d(cosu)
= -∫(0->π/2) [ 1- (cosu)^2 ]. (cosu)^2 d(cosu)
= - [(1/3)(cosu)^3 - (1/5)(cosu)^5 ]|(0->π/2)
=1/3 -1/5
=2/15
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