a maths(differentiation,40pts)

AS FOLLOW AS~~~

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y=x/cosx
dy/dx=(cosx-xsinx)/cos2x
d2y/dx2=[cos2x(sinx-xcosx-sinx)-(cosx-xsinx)(2sinxcosx)]/cos4x
=(xcos3x+2xsin2xcosx-2sinxcos2x)/cos4x
=xsecx+[2x(1-cos2x)cosx]/cos4x-2sinxsec2x
=xsecx+2xsec4x-2xsecx-2sinxsec2x
=2xsec4x-2sinxsec2x-xsecx
=secx(2xsec3x-2sinxsecx-x)
=secx(2xsec3x-2tanx-x)

y=x/sqrt(x-1)
dy/dx={sqrt(x-1)-x[1/2sqrt(x-1)]}/(x-1)
dy/dx=[2(x-1)-x]/[2(x-1)3/2
=(x-2)/2(x-1)3/2
d2y/dx2=[2(x-1)3/2-(x-2)3(x-1)1/2]/4(x-1)3
=[2(x-1)-3(x-2)]/4(x-1)5/2
=(-x+4)/4(x-1)5/2

i know the answer ...

after few mins , i will post the answer..



2008-07-02 20:14:44 補充：
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2008-07-02 20:30:44 補充：
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