Hi

look on Attachments

2. L.H.S.

$=\frac{\cos^2 z-3\cos z+2}{\sin^2 z}$

$=\frac{(1-\cos z)(2-\cos z)}{(1-\cos^2 z)}$

$=\frac{(1-\cos z)(2-\cos z)}{(1-\cos z)(1+\cos z)}$

$=\frac{(2-\cos z)}{(1+\cos z)}$

=R.H.S.

3. thanks , but can explain this steps specially the first one

4. Originally Posted by r-soy
thanks , but can explain this steps specially the first one
The numerator has been factorised, the denominator has been re-written using the Pythagorean identity.