# Thread: Finding Angles(Factor Formulae)

1. ## Finding Angles(Factor Formulae)

Find all angles between 0 and $\pi$ for which $4cos\frac{A}{2}cosAsin\frac{5A}{2}=0$

2. Hello Punch
Originally Posted by Punch
Find all angles between 0 and $\pi$ for which $4cos\frac{A}{2}cosAsin\frac{5A}{2}=0$
Given that
$4\cos\frac{A}{2}\cos A\sin\frac{5A}{2}=0$
any of these three factors could be zero. So you must solve:
$\cos\frac{A}{2}=0$
and
$\cos A=0$
and
$\sin\frac{5A}{2}=0$
Can you do that?

Grandad

3. Originally Posted by Grandad
Hello PunchGiven that
$4\cos\frac{A}{2}\cos A\sin\frac{5A}{2}=0$
any of these three factors could be zero. So you must solve:
$\cos\frac{A}{2}=0$
and
$\cos A=0$
and
$\sin\frac{5A}{2}=0$
Can you do that?

Grandad
Never Thought it to be like this, thanks

4. Just a little question if $
\sin\frac{5A}{2}=0
$
, then in what quadrants does A lies in? Does zero means that it is positive or negative?

Edit: Found out that zero is neutral and it belongs to all quadrant.