SOLUTION: Assume θ is an angle in the first quadrant, and sin(θ) = 5/7 Find cos(θ) Find cos(2θ)

Algebra ->  Trigonometry-basics -> SOLUTION: Assume θ is an angle in the first quadrant, and sin(θ) = 5/7 Find cos(θ) Find cos(2θ)       Log On


   

Question 963370: Assume θ is an angle in the first quadrant, and
sin(θ) = 5/7
Find cos(θ)

Find cos(2θ)
Answer by Fombitz(32388) About Me  (Show Source):
You can put this solution on YOUR website!
sin%5E2%28theta%29%2Bcos%5E2%28theta%29=1
25%2F49%2Bcos%5E2%28theta%29=1
cos%5E2%28theta%29=24%2F49
cos%28theta%29=0+%2B-+%282%2F7%29sqrt%286%29
Since it's in the first quadrant,
cos%28theta%29=%282%2F7%29sqrt%286%29
.
.
.
cos%282%2Atheta%29=cos%5E2%28x%29-sin%5E2%28x%29
cos%282%2Atheta%29=24%2F49-25%2F49
cos%282%2Atheta%29=-1%2F49