Question

Use Half-Angle Identity to evaluate:

Answer 1

\[\sin 105^{\circ}. \]
So far I have:
\[\sin (\frac{210}{2}) = \pm \sqrt{\frac{1-\cos\theta}{2}} . \]

What should I do now? How do I find out \[\cos\theta ? \]
Please help!!

Answer 2

Any Ideas?

Answer 3

Would you draw a 210 degree triangle?

Answer 4

Which would be a 30-60-90

Answer 5

you want sin(105) so
let theta = 210 so that sin(105) = sin(210/2)

Answer 6

Here's where I'm stuck now:

Answer 7

you can do that too... according to the formula you need cos(210) right?