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谁的导数是x的三次方cos2x

题目详情
谁的导数是x的三次方cos2x
▼优质解答
答案和解析
∫x^3cos2x dx
=(1/2)∫x^3dsin2x
=(1/2)x^3sin2x - (3/2)∫x^2.sin2x dx
= (1/2)x^3sin2x + (3/4)∫x^2.dcos2x
= (1/2)x^3sin2x + (3/4)x^2cos2x - (3/2)∫xcos2xdx
= (1/2)x^3sin2x + (3/4)x^2cos2x - (3/4)∫xdsin2x
=(1/2)x^3sin2x + (3/4)x^2cos2x - (3/4)xsin2x + (3/4)∫sin2xdx
=(1/2)x^3sin2x + (3/4)x^2cos2x - (3/4)xsin2x - (3/8)cos2x + C