sin-1 (x) = 2 tan-1(x). number of solutions are -

a) 1

b)2

c)3

d)5

   sin^-1 x=2tan^-1 x            or               sin^-1 x=sin^-1 (2x/1+x² )             .                                       or                      x=2x/1+x²              .                                                            or               x+x³ =2x                    .                                        or              x³ -x=0                           .                                hence                      x=0,-1,1 are the solutions of the equation.                                                                                                    .     therefore, number of solutions are 3.