trig problem.

[mzplp113]

sin^2(theta/2) = cos(theta)

how do i start this? do i change sin^2 to 1-cos^2? if i do, then what do i do after that?

 

[fasteddie65]

sin^2(theta/2) = cos(theta)

how do i start this? do i change sin^2 to 1-cos^2? if i do, then what do i do after that?

sin^2 (ø/2) = cos ø
(1 - cos ø)/2 = cos ø
1 - cos ø = 2 cos ø
1 = 3 cos ø
1/3 = cos ø
At this point you can use a table or a calculator to find the values of ø.

 

[chrisr]

There are often a few ways to proceed,
but you should have a "strategy".

Express the sin[sup:362rny0l]2[/sup:362rny0l](A/2) as Cos(angle).

That was done in a single step in the answer to your post and is very quick.

If you had continued on with your method,
expressing Sin[sup:362rny0l]2[/sup:362rny0l](A/2) as 1-Cos[sup:362rny0l]2[/sup:362rny0l](A/2),
then your next step would be to express the "Cosine squared" as Cosine using

Cos[sup:362rny0l]2[/sup:362rny0l](A) = 0.5(1+Cos2A), or Cos[sup:362rny0l]2[/sup:362rny0l](A/2) = 0.5(1+CosA).

This then leaves you with only Cos(theta) to solve for.