∫(sinx)^3(cosx)^5dx

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∫(sinx)^3(cosx)^5dx∫(sinx)^3(cosx)^5dx∫(sinx)^3(cosx)^5dx∫sin³xcos^5(x)dx用归约公式∫[(cosx)^m·(sinx)

∫(sinx)^3(cosx)^5dx
∫(sinx)^3(cosx)^5dx

∫(sinx)^3(cosx)^5dx
∫sin³xcos^5(x)dx
用归约公式∫[(cosx)^m·(sinx)^n]dx=
-[(cosx)^(m+1)·(sinx)^(n-1)]/(m+n)
+[(n-1)/(m+n)]∫[(cosx)^m·(sinx)^(n-2)]dx
原式=-[cos^6(x)·sin²x]/(3+5)+(2/8)∫[sinxcos^5(x)]dx
=(1/4)∫[sinxcos^5(x)]dx-(1/8)sin²xcos^6(x)
=-(1/4)∫cos^5(x)d(cosx)-(1/8)sin²xcos^6(x)
=-(1/4)(1/6)cos^6(x)-(1/8)sin²xcos^6(x)+C
=-(1/24)cos^6(x)-(1/8)sin²xcos^6(x)+C
=(1/48)cos^6(x)[3cos(2x)-5]+C

这是小学的题目吗?

sinx=t;dt=cosdx,有
∫sin^3xcos^4xcosxdx=∫t^3(1-t^2)^2dt
=∫(t^3-2t^5+t^7)dt=1/4t^4-1/3t^6+1/8t^8+C
=1/4(sinx)^4-1/3(sinx)^6+1/8(sinx)^8+C