Which of the following formula is incorrect?

[answerhappygod]

a) sin-1⁡x+sin-1⁡y=sin-1⁡{\(x\sqrt{1-y^2}+y\sqrt{1-x^2}\)}
b) sin-1⁡x-sin-1⁡y=sin-1⁡{\(x\sqrt{1+y^2}+y\sqrt{1+x^2}\)}
c) 2 tan-1⁡x=tan-1⁡\((\frac{2x}{1-x^2})\)
d) 2 cos-1⁡x=cos-1⁡(3x-4x3)