Posted by Amy on .
solve cos 5 thetha cos 15 sin5theta sin 15 =squareroot of 3/2
Thank you

PreCal 
drwls,
Remember that
cos(a+b) = cosa cosb  sina sinb
Therefore
cos5theta*cos 15 sin5theta*sin 15
= squareroot of 3/2
cos(5theta + 15)
= cos^1(sqrt3)/2
Take the arccosines of both sides
5 theta + 15 = 30 degrees5 theta = 15 degrees
theta = 3 degrees