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高数(分部积分法)问题= =

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高数(分部积分法)问题= =
1 ∫e^x乘以(cosx)^2 dx
2 ∫e^arcsinx dx
3 ∫(sinx)^6 dx 区间-π/2到π/2
1.cos²x = 1/2 + cos(2x) /2
∫ e^x [1/2 + cos(2x) /2] dx = (1/2) e^x + (1/2) ∫ e^x cos(2x) dx
I = ∫ e^x cos(2x) dx = ∫ cos(2x) d(e^x ) = e^x cos(2x) - ∫ e^x [-2 sin(2x)] dx
= e^x cos(2x) + ∫ 2 sin(2x) d(e^x)
= e^x cos(2x) + 2e^x sin(2x) - 4 ∫ e^x cos(2x) dx
=> I = (1/5) [e^x cos(2x) + 2e^x sin(2x) ] + C
原式 = (1/2) e^x + (1/10) [e^x cos(2x) + 2e^x sin(2x) ] + C
2.I = x * e^arcsinx - ∫ e^arcsinx * x/√(1-x²) dx = x * e^arcsinx + ∫ e^arcsinx d√(1-x²)
= x * e^arcsinx + √(1-x²) e^arcsinx - I
=> I = (1/2) e^arcsinx [ x + √(1-x²) ] + C
3.∫ [-π/2,π/2] (sinx)^6 dx = 2 ∫ [0,π/2] (sinx)^6 dx 有递推公式
= 2 * [ 5*3*1 /(6*4*2)] * π/2
= π/16