# Homework Help: Prove cosign problem

1. Sep 3, 2008

### ritwik06

1. The problem statement, all variables and given/known data
Prove that:
$$\sqrt{3}cos 20 - sec 40=4$$

3. The attempt at a solution
Assuming th statement to be true;
$$\sqrt{3}cos 20 - \frac{1}{2cos^{2}20 - 1}=4$$

$$2\sqrt{3}cos^{3} 20- 8 cos^{2} 20 -\sqrt{3}cos 20+3=0$$

It results in a cubic equation???? Help

2. Sep 3, 2008

### Defennder

Re: Trigonometry

Problem with this question is that it's not even true for both radians and degrees. Try it on your calc.

3. Sep 3, 2008

### Dick

Re: Trigonometry

That is an excellent point. I hadn't even thought to try it. Duh.

4. Sep 4, 2008

### ritwik06

Re: Trigonometry

Sorry guys it was a type error!

5. Sep 4, 2008

### snipez90

Re: Trigonometry

Eh, if that 0 was a theta, it looks solvable.

6. Sep 5, 2008

### Defennder

Re: Trigonometry

Yeah, but it reads "prove that..." and not "solve..."