I am not understanding how to solve this one, so any help would be greatly appreciated!

Problem: An isosceles triangle has equal sides of length 10 cm and a base of 8 cm. Find the angles of the triangle. Hint: draw a perpendicular bisector at the base.

Here's where I started- i have two right triangles, bisected, so working with one triangle I have a hypotenuse of 10 cm and a base of 4. I know I need to use the COS (4/10), but I was not sure if it needed to be an inverse COS to get the angle. I got an angle of 66.4 degrees, but I am not sure if I solved that right. (I am not in trig, our teacher just did a short intro to right triangle trig and now i'm stuck.)