21-2 求导7.y=sin^nx(sin的n次方x)8.y=cos^3 x/2(cos的3次方x/2)9.y=lnta
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7.y=(sinx)^n

dy/dx=n[(sinx)^(n-1)]cosx

8.y=(cos½x)³

dy/dx=3(cos½x)²(-sin½x)½

=-(3/2)(cos½x)²(sin½x)

or =-(¾)sinxcos½x

9.y=lntan½x

dy/dx=(1/tan½x)(sec½x)²½

=½(cot½x)(sec½x)²

=½(csc½xsec½x)

=1/sinx=cscx

10.y=lnlnx

dy/dx=(1/lnx)(1/x)=1/(xlnx)

11.y=1/cos^n x(cos的n次方x)

dy/dx=-[n/(cosx)^(n+1)](-sinx)

=nsinx(secx)^(n+1)

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