Trig hep, please? Thank you!
posted by Michelle on .
1. Find the exact value of sin(195(degrees))
2. If cot2(delta)=5/12 with 0(<or =)2(delta)pi, find cos(delta), sin(delta) , tan(delta).
3.find the exact value of sin2(x) if cos(x)= 4/5. (X is in quadrant 1)
4. Find the exact value of tan2(x) if sin(x)=5/13. ((X) in quadrant 2)
5. Solve sin2(x)+sin(x)=0 for 0<or=x<or=2pi.
6. Write 2sin37(degrees)sin26(degrees) as a sum (or difference).

1.
sin 195°
=  sin15° , by CAST
we know cos 30° = 1  2 sin^2 15°
√3/2 = 1  2sin^2 15°
2sin^2 15 = 1  √3/2 = (2√3)/2
sin^2 15° = (2√3)/4
sin 15 = √((2√3)) /2
so sin 195
= sin15
= √((2√3)) /2
3. given cos x = 4/5 , x in I
then by Pythagoras, sinx = 3/5
sin 2x = 2sinx cosx
= 2(3/5)(4/5) = 24/25
5.
sin 2x + sinx = 0 , 0 ≤ x ≤ 2π
2sinxcosx + sinx = 0
sinx(2cosx + 1) = 0
sinx = 0 or cosx = 1/2
x = π/2
x = 3π/2
x = ππ/3 = 2π/3  ( 120°)
Give the others a try, let me know what you got
x = π+π/3 = 4π/3  (240°) 
thanks! what do the question marks stand for.
and also CAST? 
I will try the others soon.