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∫xCosx/sin^3xDx

原式=∫xdsinx/cos³x =∫xd[-1/(2sin²x)] =-1/2xcsc²x-1/2*∫(-csc²x)dx =-1/2xcsc²x-1/2*cotx+C

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limx→0 (sinx-xcosx)/sin^3x =(1-xcotx)/sin²x =(tanx-x)/x³ 利用等价无穷小:sinx∽x∽tanx =(sec²x-1)/3x² 洛必达法则,上下求导 =tan²x/3x² =1/3 利用等价无穷小:x∽tanx

lim(x→0)(sinx-xcosx)/(sin^3x) =lim(x→0)[(sinx-xcosx)]'/(sin^3x)' =lim(x→0)(cosx-cosx+xsinx)/[3(sin^2x)cosx] =lim(x-0) x/[3(sinxcosx)] =lim(x-0) x/[3sin(2x)/2] =lim(x-0) x'/[3sin(2x)/2]' =lim(x-0) 1/[3cos(2x)] =1/3

∫ cos²x/sin³x dx = ∫ cot²x * cscx dx = ∫ (csc²x - 1) * cscx dx = ∫ csc³x dx - ∫ cscx dx = ∫ csc³x dx - ln|cscx - cotx| 记A = ∫ csc³x dx = ∫ cscx * csc²x dx = ∫ cscx d(- cotx) = - cscxcotx...

解: sin³x-cos³x =(sinx-cosx)(sin²x+sinxcosx+cos²x) =(sinx-cosx)(1+sinxcosx) =sinx+sin²xcosx-cosx-sinxcos²x =sinx-cosx+½sinxsin2x-½cosxsin2x =sinx-cosx-¼(cos3x-cosx)-¼(sin3x+sin...

这是奇函数在对称区间的定积分,答案一定是0,不用计算。

∫(sinx)^3.(cosx)^5dx = ∫-(1-(cosx)^2) (cosx)^5 dcosx = (cosx)^8/8 - (cosx)^6/6 +C

lim(x→0)(sinx-xcosx)/(sin^3x)=lim(x→0)[(sinx-xcosx)]'/(sin^3x)'=lim(x→0)(cosx-cosx+xsinx)/[3(sin^2x)cosx]=lim(x-0) x/[3(sinxcosx)]=lim(x-0) x/[3sin(2x)/2]=lim(x-0) x'/[3sin(2x)/2]'=lim(x-0) 1/[3cos(2x)]=1/3

sinx-cosx=½ sin²x-2sinxcosx+cos²x=¼ ∴sinxcosx=⅜ sin³x-cos³x=(sinx-cosx)(sin²x+sinxcosx+cos²x) =½(1+⅜) =11/16

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