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∫『0,x』f(t)dt = 2e^x
两边对x取导
f(x) = 2e^x
则f(-cosx) = 2e^(-cosx)
∫『0,π/2』f(-cosx)sinx dx
=∫『0,π/2』2e^(-cosx)sinx dx
=∫『0,π/2』2e^(-cosx) d(-cosx)
=∫『0,π/2』2 d(e^(-cosx))
=2e^(-cosx)『0,π/2』
=2e^(-cosπ/2) - 2e^(-cos0)
=2 - 2/e
=2(e-1)/e
两边对x取导
f(x) = 2e^x
则f(-cosx) = 2e^(-cosx)
∫『0,π/2』f(-cosx)sinx dx
=∫『0,π/2』2e^(-cosx)sinx dx
=∫『0,π/2』2e^(-cosx) d(-cosx)
=∫『0,π/2』2 d(e^(-cosx))
=2e^(-cosx)『0,π/2』
=2e^(-cosπ/2) - 2e^(-cos0)
=2 - 2/e
=2(e-1)/e
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