Sunday
May 19, 2013

# Homework Help: Trigonometry

Posted by Savannah on Monday, January 16, 2012 at 3:51pm.

2cos^2(x) = 13sinx - 5

How do i solve for x?

I think i have to use the sin^2x + cos^2x = 1, but I'm not sure how to use that. I thought about maybe doing 2(1-sin^2x) = 13sinx - 5 but then i get stuck. Any suggestions?

• Trigonometry - Damon, Monday, January 16, 2012 at 3:56pm

2 (1-sin^2 x) = 13 sin 5 - 5

2 - 2 sin^2 x = 13 sin x - 5

2 sin^2 x + 13 sin x - 7 = 0

let z = sin x

2 z^2 + 13 z - 7 = 0

(2z -1)(z+7) = 0

sin x = 1/2 or sin x = -7
-7 is not allowed, beyond range of sin function
so x = 30 degrees

• Trigonometry - Savannah, Monday, January 16, 2012 at 4:06pm

Oh that makes sense. That 2sin^2x + 13sinx - 7 can be factored. Thanks!

Related Questions

math - the problem is 2cos^2x + sinx-1=0 the directions are to "use an ...
Math, derivatives - f(x) = x² + 2Cos²x, find f ' (x) a) 2(x+cos x...
Math - Solving for Trig Equations - Solve the following equation for 0 less than...
Trigonometry - Need help solving problems using the Trigonometric Identities: ...
Math (trigonometry) - Trigonometry identities are so hard... I need some help ...
math - how would you find the angle to (3)^.5sin(2x)-2cos(2x)+2sin^2(x)=1 I know...
trig - find the exact solutions 2cos^2x+3sinx=0 the way it stands, that is a &...
MATH ANALYSIS - How do you simplify these questions?: 1. cos^2(x/2)-sin^2(x/2) 2...
Trigonometry - I have some trigonometric equations to do, but I'm pretty ...
Trigonometry - If A + B + C = 180°, Prove that Sin² (A/2) + sin² (...