# Math Help - Trigonometry

1. ## Trigonometry

The expression $\frac{cosx-cos3x}{sen3x-senx}$ is equal the:

a) $-tgx$

b) $-cotg2x$

c) $tg2x$

d) $cotg2x$

e) $tgx$

2. What is this wacky notation?. I assume sen means sin and tgx mean tanx?.

Going with that:

$\frac{cos(x)-cos(3x)}{sin(3x)-sin(x)}=\frac{2sin(x)cos(x)}{2cos^{2}-1}=\frac{sin(2x)}{cos(2x)}=tan(2x)$

3. Thank you very much