Suppose a triangle has two sides of length 3 and 4 and that the angle between these two sides is 60°. What is the length of the third side of the triangle?

For apex the answer is square root 13

There is many way how to get the length of a triangle. You can use many method but to your question the best method to use is Law of sine and cosine Side Angle Side triangle formula. This formula is this one (a^2 = b^+c^2-2bc*cos (angle)). So if your fill it up it would be (a^2 = 3^2+4^2-2*3*4*cos (60)). The answer would be 3.61