Question

please help!
k = (cos 25° cos 35°) / (cos 10° sin 20°) .
so, cos 10° equal to....

a. (k√3+1)/(2k-2)
b. (k√3+1)/(2k+1)
c. (k√3+1)/(2k+2)
d. (k√3+1)/(k+1)
e. (k√3+1)/(k-1)
(choose one option that is correct and give the explanation)