If you know all the trig identities you don't need to solve 14. The trig identities you need to know are tan=sin/cos. Sec=1/cos. And 1+tan^2= sec^2
(I'll be replacing theta with x to make it easier to type)
Problem: sinx=tanx/sqrt 1+tanx^2.
Since 1+tanx^2=secx ^2
Sinx=tanx/sqrt secx^2
Sinx=tanx/secx
Now tanx= sinx/cosx and secx=1/cosx
(Sinx/cosx)/(1/cosx). The cosx cancel out leaving sin
So sinx=sinx