using the substitution x= tan a, show that

y = tan-1 2x /1+x2

reduces to

y = 2 tan-1 x

this is what i have done:-

tan y = 2x/1+x2

tan y = 2 tan a / 1 + tan2 a

tan y = 2 tan a / sec2 a

tan y = 2sin a cos a = sin 2a

i cant work this out further...can you help me plz?