I dont know how to find the exact value of something(trig)...e.g.

sec(13Pi/6) I get a long decimal(1.31...) but how am I meant to get the exact value answer which in this case is 2/3 of the square root of 3. (which is 1.31 when u calculate it but when I see 1.31 how am I meant to know that its 2/3 the square root of 3?

question 2:

3(tan^2 )theta - sec theta = 1

for 0 <= theta =< 2PI

can anyone solve that for me? thanks

oh and for the following graph sketches:

y = sin3x

y = |sin3x|

y = sin|3x|

so like I was confused to whether they amplitude was 3 times bigger or the frequency is like 3 times smaller for them. can someone tell me what the difference of those curves are from a normal sinx