SOLUTION: Can't get this one, any help would be great, thanks. The length of a rectangle is 5 cm more than 4 times its width. If the area of the rectangle is 76 cm2, find the dimensions

Algebra ->  Quadratic Equations and Parabolas  -> Quadratic Equations Lessons -> SOLUTION: Can't get this one, any help would be great, thanks. The length of a rectangle is 5 cm more than 4 times its width. If the area of the rectangle is 76 cm2, find the dimensions       Log On


   

Question 108995: Can't get this one, any help would be great, thanks.
The length of a rectangle is 5 cm more than 4 times its width. If the area of the rectangle is 76 cm2, find the dimensions of the rectangle to the nearest thousandth.
Answer by Fombitz(32388) About Me  (Show Source):
You can put this solution on YOUR website!
Area of a rectangle : A=L%2AW=76
L=5+4W
Substitute in the area equation.
L%2AW=76
((((5+4W)*W=76}}}
5W%2B4W%5E2=76
4W%5E2%2B5W-76=0
Use the quadratic formula,
W+=+%28-b+%2B-+sqrt%28+b%5E2-4%2Aa%2Ac%29%29%2F%282%2Aa%29
W+=+%28-5+%2B-+sqrt%28+5%5E2-4%2A4%2A%28-76%29+%29%29%2F%282%2A4%29
W+=+%28-5+%2B-+sqrt%28+1241+%29%29%2F%288%29
Since a negative width doesn't make sense, we will only use the positive root.
W+=+%28-5+%2B+sqrt%28+1241+%29%29%2F%288%29
W+=+%28-5+%2B+35.22783%29%2F%288%29
highlight%28W=3.778%29
L=5%2B4W
L=5%2B4%2A%283.778%29
L=5%2B15.114
highlight%28L=20.114%29
Verify the area to check your answer.
A=L%2AW=76
%283.778%29%2820.114%29=76
%2875.991%29=76
Close enough, true statement.
Good answer.