设y=(1+sin x)x,则dy∣x=π=

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问题 设y=(1+sin x)x,则dy∣x=π=

选项 A、-πdx   
B、πdx   
C、-2πdx
D、2πdx

答案A

解析 因y=(1+sin x)x=exln(1+sin x),则
dy=exln(1+sin x)d[xln(1+sin x)]
=(1+sin x)x{ln(1+sin x)dx+xd[ln(1+sin x)]}
=(1+sin x)x[1n(1+sin x)dx+d(sin x)]
=(1+sin x)x[1n(1+sin x)dx+dx]
=(1+sin x)x[ln(1+sin x)+]dx,
所以dy∣x=π=(1+sinπ)x ln(1+sinπ)+]dx=-πdx.选A.
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