Identities

[edd fedds]

I'm kinda stuck on these three identity Questions: Could you explain how to solve these to me. Please and Thankyou.

6. Find the exact value of sin 2 ? given that cos ? = 12/13 and ? is in Quadrant I.
a. -120/169
b. 120/169
c. 60/169
d. -60/169

8. Find the value of the tan of a/2 given that cos a = -4/5 and a is in Quadrant II.
a. 3
b. 1/2
c. -2
d. -1/2

14. Evaluate sin 165 ° + sin 105 ° .

 

[BigGlenntheHeavy]

$\displaystyle Hints$

$\displaystyle 6) \ sin(2\theta) \ = \ 2sin(\theta)cos(\theta)$

$\displaystyle 8) \ tan\bigg(\frac{a}{2}\bigg) \ = \ \frac{1-cos(a)}{sin(a)}$

$\displaystyle 14) \ sin(u)+sin(v) \ = \ 2sin\bigg(\frac{u+v}{2}\bigg)cos\bigg(\frac{u-v}{2}\bigg)$

 

[edd fedds]

Thanx! :mrgreen: