If a rectangular prism has a length of l, a width of w, and a height of h, then the length of its diagonal is equal to sqrt(l^2+w^2+h^2). Suppose l=3 and h=12; if the length of the diagonal is 13, what is the width?
sqrt (32 + 122 + w2 ) = 13 square both sides
w2 = 132 - 32 - 122 Take it from here !