A rectangular deck has an area of 320ft^2. the length of the deck is 4 feet longer than the width. find the dimensions of the deck. solve by completing the square.

A = L * W

A = 320

L = W + 4

320 = W (W + 4)

320 = W^2 + 4W

W^2 + 4W = 320

W^2 + 4W + 4 = 320 + 4

(W + 2) ^2 = 324

W + 2 = (+-) sqrt 324

W = - 2 (+-) 18

W = - 2 + 18 = 16 ft < = = this is the width

W = - 2 - 18 = - 20 ... not this one because it is negative

L = W + 4

L = 16 + 4

L = 20 ft < = = = this is the length

in summary ... the width is 16 ft and the length is 20 ft