Quadratic Formula Question

Question

 The perimeter of a rectangle is 42 m. What are the dimensions of the rectangle if its area is 80 sq. m? You can use math.typeit.org to type, copy and paste the standard form of a quadratic equation you can use to solve the problem; then type in the two dimensions in the correct order. Add units. 

Answer 1

Lw = 80

L+w = 42/2 = 21

L =21-w

(21-w)w = 80

21w -w^2 = 80

w^2 -21w +80 = 0

w = 21/2 +/-.5sqr(441-320)

w = 10.5 +/-.5(sqr121)

= 10.5+/-5.5

= 16 or 5

L= 5 or 16

dimensions are 5 by 16 meters

5x16= 80 m^2 = area

2(5+16)=42 m = perimeter