Posted by **Kindell** on Monday, March 17, 2008 at 2:15am.

2cos*2x-cosx=1 find all solutions to the equation on the domain [0,2ð]

i got ð/4, 7ð/4, 3ð/4, and 5ð/4 but only got two out of four points... what did i do wrong?

- Pre Cal -
**drwls**, Monday, March 17, 2008 at 6:25am
Is cos*2x supposed to mean cos^2 x?

Is 2ð supposed to mean 2 pi?

If so,

2 cos^2x - cos x -1 = 0

which factors into

(2 cos x +1)(cos x -1) = 0

The solutions occur where cos x = -1/2 or +1

If cos*2x means cos(2x), then

2[2 cos^2 x -1) - cos x -1 = 0

4 cos^2 x -cos x -3 = 0

(4 cosx +3)(cosx - 1) = 0

x is where cos x = -3/4 or +1

## Answer This Question

## Related Questions

- Pre-Cal(Please check) - Approximate the equation's solutions in the interval (0,...
- pre cal--check - Name all the values of x that are not in the domain of f(x) = (...
- Precalculus - Please help!!!!!!!!!!! Find all solutions to the equation in the ...
- pre-cal - find all solutions in interval [0,2pi] tan²x = -3/2 secx This question...
- Pre-Algebra - Equation M: y = 3x + 4 Equation P: y = 3x + 7 Which of the ...
- math,correction - Find four solutions for the equation 3x+5y=15 so the equation ...
- Trig....... - I need to prove that the following is true. Thanks (2tanx /1-tan^x...
- Pre-Cal - Find all the solutions of the equation in the interval (0,2pip) sin(x...
- Pre-Cal(Urgent!!) - Find all the solutions of the equation in the interval (0,...
- Pre-Cal - Approximate the equation's soultions in the interval (o, 2pi). If ...

More Related Questions