Find the zeroes of r. What to do when it is a multiple of theta?

[Tyrion101]

I understand what to do when theta is by itself such as r=5+10cos(theta) but what if you have the same equation, and it is (2theta) I am on taptalk by the way.

 

[Mark44]

I understand what to do when theta is by itself such as r=5+10cos(theta) but what if you have the same equation, and it is (2theta) I am on taptalk by the way.

What have you tried?
In essence, you're trying to solve the equation $5 + 10\cos(2\theta) = 0$.

 

[Tyrion101]

Well if it were without the 2*theta I'd set it equal to 0, like you did, and solve for cos(theta). Well anyway without the 2 you turn the equation into cos=-1/2, would I just multiply -1/2 by 2? Or would I add 2pi or something?

 

[symbolipoint]

Solve for 2*theta. Solve for theta from that.

 

[Mark44]

Well if it were without the 2*theta I'd set it equal to 0, like you did, and solve for cos(theta). Well anyway without the 2 you turn the equation into cos=-1/2, would I just multiply -1/2 by 2? Or would I add 2pi or something?

You took a trig class, right? Do you still have your textbook? If so, there should be numerous examples of solving trig equations, including ones that involve the sine or cosine (or other trig function) of angle multiples.