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ΪʲôCosx+Cox3x=2Cos2x*Cosx

cos2x-x+cos2x+x =cos2xcosx+sin2xsinx+cos2xcosx-sin2xsinx =2cos2xcosx

lim (cosx-cos3x)/x² x0 =lim 2sin2xsinx/x² x0 =lim 22sinxcosxsinx/x² x0 =lim 4x²cosx/x² x0 =lim 4cosx x0 =4cos0 =41 =4

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١[1/(a^2+x^2)]dx x=atanx =[1/(a^2+a^2(tanx)^2)]dx=(1/a^2)(cosx)^2dx=(1/a^2)[(cox2x+1)/2 ] dx =(1/2a^2)[(sin2x)/2+x] ڷĸӶ0ش﷨ ԭʽ=lim(x0) ln(1+3x)/2x ش =lim(x0) 3/2(1+3x)=3/2

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