高等数学。计算下列定积分。

如题所述

(1)
let
y=t^2
dy =2tdt
t=0, y=0
t=√x, y=x

∫(0->√x ) t.sin(t^2) dt
=(1/2)∫(0->x ) siny dy
=(1/2) ( cosx -1 )

(2)
∫(0->π/2 ) (cosx)^5. sinx dx
=-∫(0->π/2 ) (cosx)^5. dcosx
=-(1/6)[ (cosx)^6] |(0->π/2 )
=1/6

(3)

let
y=x-1

∫(0->2 ) |x-1| dx
=∫(-1->1 ) |y| dy
=-∫(-1->0 ) y dy +∫(0->1 ) y dy
=- (1/2) [y^2]|(-1->0) + (1/2) [y^2]|(0->1)
=1
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