Question...
For the Half-Angle Problems:
how do you know if the answer is positve or negative...
(i circled it in RED)
It depends in which quadrant is $\displaystyle \frac{a}{2}$.Originally Posted by CONFUSED_ONE
NOT $\displaystyle a$ but $\displaystyle \frac{a}{2}$.
If $\displaystyle \frac{a}{2}$ is in the first or second quadrant then you use positive, otherwise use the negative.
Your question, is a classic mistake which I seen many people make, hopefully you will not make it.
I presume that is in radians?Originally Posted by CONFUSED_ONE
The first and second quadrant span $\displaystyle 0^o\leq x\leq 180^o$
Or in Radians, $\displaystyle 0\leq x\leq \pi$
Since,
$\displaystyle 0\leq .4\leq 3.14$ it is in the first and second quadrants.
In fact it is in first quadrant because it spans,
$\displaystyle 0\leq x\leq \frac{\pi}{2}\approx 1.57$