Question

the length of a rectangle is 6 meters less than twice the width. The area of the rectangle is 140m². Find the dimensions of the rectangle.

Answer 1

Answer:

Here's what we know:

A = Lw (Area is length times width)

L = 2w + 6 (length is twice the width plus 6)

A = 140 (Area is 140 m2)

Plug in the variable values:

140 = w(2w + 6)

Distribute:

140 = 2w2 + 6w

Subtract 140:

2w2 + 6w - 140 = 0

Factor out a 2:

2(w2 + 3w - 70) = 0

Divide both sides by 2:

w2 + 3w - 70 = 0

(w + m)(w - n)

When we factor out the quadratic, we know it's going to be a +/- situation because the c value in the quadratic is negative, and the two numbers are going to be three away, the plus next to the 3 meaning that the larger number is going to be positive:

(w + 10)(w - 7) = 0

w = -10, 7

We can't have a negative length, so we can toss out the -10, leaving us with w = 7 meters.

L = 2 * 7 + 6

L = 14 + 6

L = 20

Check:

140 = 20 * 7

140 = 140

Answer 2

Equation 1 is 2W - 6 = L
equation 2 is 140= W * L

L=10
W=8