Explanation:
We're applying the dot product.
u dot v = 3*(-4) + (-8)*8
u dot v = -12 - 64
u dot v = -76
The idea is that we multiply the x coordinates together, and the y coordinates together separately. Afterward you add the products. The result of any dot product is a scalar value, aka a single number.
The dot product is useful in many applications. One of which is to determine if two vectors are orthogonal.
