Wednesday

March 4, 2015

March 4, 2015

Posted by **caitlyn** on Tuesday, April 26, 2011 at 9:14pm.

- pre calc -
**MathMate**, Tuesday, April 26, 2011 at 9:42pmcos2x-cosx=0

expand the left hand side

cos²(x)-sin²(x)-cos(x)=0

2cos²(x)-1 - cos(x)=0

substitute c=cos(x)

2c²-c-1=0

c=(-1±√(9))/4

=-1 or 1/2

cos(x)=-1 when x=π (0≤x≤2π)

or

cos(x)=1/2 when x=π/3 or x=5π/3 (0≤x≤2π)

Substitute each of the three solution into the original equation to make sure that the solutions are acceptable.

- pre calc -
**MathMate**, Tuesday, April 26, 2011 at 9:57pmReiny is right.

There was a mistake in the solution of the quadratic.

c=(1±√(9))/4

=1 or -1/2

cos(x)=1 when x=0 or 2π (0≤x≤2π)

or

cos(x)=-1/2 when x=π±π/3 (0≤x≤2π)

Substitute each of the three solution into the original equation to make sure that the solutions are acceptable.

**Answer this Question**

**Related Questions**

Pre calc - Find solutions on interval 0,2pie (cosx/1+sinx) + (1+sinx/cosx) = -4

identities trig? - find all solutions to the equation in the interval [0,2pie] ...

Precalculus - Please help!!!!!!!!!!! Find all solutions to the equation in the ...

pre-calc - Solve: cos(2x-180) - sin(x-90)=0 my work: cos2xcos180 + sin2xsin180= ...

Pre Calc - Solve the equation on the interval [0,2pi). cos2x=(*2/2)

Pre Calc - Solve the equation on the interval [0,2pi). cos2x=(*2/2)

Pre-Calc - Trigonometric Identities Prove: (tanx + secx -1)/(tanx - secx + 1)= ...

Pre-Calculus - Find all solutions to the equation in the interval [0, 2pi) cos4x...

Trigonometry - Solve for x in the interval 0<=x<360: 1. 2sin2x+cosx =0 2. ...

Advanced Math - Could someone help me with those two questions. I need to know ...