y=cosf(x²)y'=-sinf(x²) *f'(x²)*2x=-2xf'(x²)sinf(x²)y"=-2[f'(x²)sinf(x²)+2x²f"(x²)sinf(x²)+xf'(x²)cosf(x²)*f'(x²)*2x]=-2[f'(x²)sinf(x²)+2x²f"(x²)sinf(x²)+2x²f'²(x²)cosf(x²)]
