Prove that mn < 0 if and only if m > 0 and n < 0 or m < 0 and n > 0

The base of a triangle exceeds the height by 7 centimeters. if the area is 400 square centimeters, find the length of the base and the height of the triangle.

1) what is the measure of the exterior angle, ∠uvw ? 2) in triangle man, what is the measure of the exterior angle at n (in degrees)?

Given that abcd is a rhombus, what is the value of x?