To show that
cos-1(-x)-cos-1(x)=2sin-1(x)
I tried
take x= sina
taking cos of the whole equation
cos(cos-1(-x))-cos(cos-1(x))=2cos(sin-1(x))
now we have to prove : -x-x=2cos(sin-1(x))
LHS: -2x=-2sina=2cos(a+pi/2)
RHS: 2cosa
Iam not sure how to proceed further..can anyone help me...