1)y`=(-sinx(cosx-1)+sinx(cosx+1))/(cosx-1)²=(-sinxcosx+sinx+sinxcosx+sinx)/(cosx-1)²=
=2sinx/(cosx-1)²
2)y`=2x/2√(1+x²)=x/√(1+x²)
y``=(√(1+x²) -x*2x/2√(1+x²))=1/(1+x²) (1+x²-x²)/√(1+x²)³=1/(1+x²)
3)y`=-1/sin²x2sinxcosx/(sinx)^4=2cosx/sin³x
y``=2sinxcosx/(sinx)^4=2cosx/sin³x
y```=(-2sinx *sin³x -2cosx*3sin²x*cosx=(-2(sinx)^4 -6sin²xcos²x)/(sinx)^6=
=-2sin²x(sin²x+3cos²x)/(sinx)^6=-2(sin²x+3cos²x)/(sinx)^4=-2(3-2sin²x)/(sinx)^4