I'm not sure how to prove these expressions true...the question is:

Prove that each expression is an identity for all values for which it is defined.

$\displaystyle

\frac {sin\theta} {sin\theta+cos\theta} = \frac {tan\theta} {1+tan\theta}

$

and,

$\displaystyle

\frac {sin^2\theta+2cos\theta-1} {sin^2+3cos\theta-3} = \frac {1} {1-sec\theta}

$

Thank you!