Homework Statement
Find the determinant of the matrix {{cos 25°, sin° 65}, {sin 120°, cos 390°}} (sorry, can't latex). {cos 25°, sin° 65} is first row and {sin 120°, cos 390°} is the second one.
Homework Equations
cos(a + b) = (cos a)(cos b) - (sin a) (sin b)
The Attempt at a...