# Trigo-sign

• June 21st 2009, 09:03 AM
dhiab
Trigo-sign
• June 21st 2009, 11:13 AM
HallsofIvy
Quote:

Originally Posted by dhiab

$cos(x)+ \sqrt{3} sin(x)= 0$ when $tan(x)= \frac{sin(x)}{cos(x)}= \frac{1}{\sqrt{3}$ and that happens when $x= \pi/6+ k\pi$. $sin^2(x)- 1/2= 0$ when $sin(x)= \pm\frac{1}{\sqrt{2}}$ and that happens when $x= k\pi/4$. Those points are the only places you expression can change sign.