SOLUTION: csc theta = sqrt(31). What would cos(2theta) equal?

Algebra ->  Trigonometry-basics -> SOLUTION: csc theta = sqrt(31). What would cos(2theta) equal?      Log On


   

Question 821921: csc theta = sqrt(31). What would cos(2theta) equal?
Answer by lwsshak3(11628) About Me  (Show Source):
You can put this solution on YOUR website!
csc theta = sqrt(31). What would cos(2theta) equal?
cscx=√31
sinx=1/√31=√31/31
Identity:cos2x=1-2sin^2x)=1-2*31/961)=1-(62/961)=899/961
..
calculator check:
sinx=√31/31
x≈10.35˚
2x≈20.69˚
cos2x=cos(20.69)≈0.935..
exact value as calculated=899/961≈0.935..