Monday

April 21, 2014

April 21, 2014

Posted by **Greg** on Tuesday, January 14, 2014 at 10:55pm.

π/8

-7π/4

15π/4

3π/4

- TRIG help quickly please -
**Reiny**, Tuesday, January 14, 2014 at 11:22pm2 cos (2x) - 1 = 0

cos (2x) = 1/2

2x = π/3 or 2x = 2π-π/3 or 5π/3

x = π/6 or x = 5π/6

none of the given answers apply

I will assume you meant

2 cos^2 x - 1 = 0

by definition:

2cos^2 x -1 = cos (2x)

so cos(2x) = 0

2x = π/2 or 2x = 3π/2

x = π/4 or x = 3π/4

I see one of those answers. 3π/4

looking at the others, note that -7π/4 is coterminal with π/4

so it would be a solution as well

**Related Questions**

Trig - find all solutions to the equation √3 csc(2theta)=-2 Would the ...

Trig - The set of solution(s) of 2 cos^2 (θ) - 13 cos(θ) + 6 = 0 that ...

Trig Help! - Question: Trying to find cos π/12, if cos π/6 = square ...

Calculus - How do I find the critical values? y= 4/x + tan(πx/8) What I ...

Precalculus - Use one of the identities cos(t + 2πk) = cos t or sin(t + 2&#...

Math integrals - What is the indefinite integral of ∫ [sin (π/x)]/ x^...

Math - Evaluate *Note - We have to find the exact value of these. That I know to...

geometry/algebra - I asked this question yesterday, and I'm trying to understand...

Trig - Solve the trig equation exactly over the indicated interval. tanθ = ...

Calculus - an open topped cylinder has a volume of 125 cubic inches. determine ...