trigonometry
posted by Alonso .
5. If cot 2θ = 5/12 with 0 ≤ 2θ ≤ π , find cosθ, sinθ, and tanθ
8. Find the exact value of sin2a if cosa = 4/5(a in Quadrant I)
13. Find the exact value of tan2 if sinB = 5/13 (B in quadrant II)
14. Solve sin 2x + sin x = 0 for 0 ≤ x ≤ 2π.
21. Write 2sin37°sin26° as a sum (or difference).

trigonometry 
Steve
5.
since cot(x) < 0 in QII, 2θ is in QI
so, we have a 51213 triangle in QI.
8.
we have a 345 triangle, so sina = 3/5
13.
again, a 51213 in QII, so y>0 and x<0
14.
review sumtoproduct formulas:
sin u + sin v = 2 sin(½(u+v)) cos(½(u−v))
21. review producttosum formulas:
sin A sin B = ½ cos(A−B) − ½ cos(A+B)
If you get stuck, or want to check your answers come on back.
If stuck, where do you run aground? Remember to draw the triangles where involved, paying attention to quadrants.
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