if tan x=5/3

a) What is the value of sin (2x)

b) What is the value of cos (2x)

my awnser have to be in fraction

Im not allowed to use a calculater to get an awnser and im unsure what im suppose to do...

I think that sin x=5

and cos x=3

but i really don't know...

Thanks in advance

Janne the Swede