# Math Help - Help me to solve thisTrigonometry problem

1. ## Help me to solve thisTrigonometry problem

if K = $\frac{cos 25.cos35}{sin10.sin20}$ then the value of $cos10$ = ?

2. Originally Posted by wizard654zzz
if K = $\frac{cos 25.cos35}{sin10.sin20}$ then the value of $cos10$ = ?

HI

$K=\frac{\frac{1}{2}[\cos 60+\cos 10]}{-\frac{1}{2}[\cos 30-\cos 10]}$

$=\frac{\cos 60+\cos 10}{\cos 10-\cos 30}$

$=\frac{\frac{1}{2}+\cos 10}{\cos 10-\frac{\sqrt{3}}{2}}$

$
\cos 10=\frac{k\sqrt{3}+1}{2(k-1)}
$