SOLUTION: the length of a rectangle is 7 cm less than three times its width. its area is 20 square centimeters. Please help me find the dimensions of the rectangle.

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Question 1131620: the length of a rectangle is 7 cm less than three times its width. its area is 20 square centimeters. Please help me find the dimensions of the rectangle.
Answer by MathLover1(20850) About Me  (Show Source):
You can put this solution on YOUR website!
let the length be L and te width W
if the length of a rectangle is 7cm less than three+times its width, we have
L=3W-7 ........eq.1

if its area is 20cm%5E2, we have
L%2AW=20........substitute L from eq.1
L%2AW=20
%283W-7%29%2AW=20
3W%5E2-7W=20
3W%5E2-7W-20=0........factor
3W%5E2-12W%2B5W-20=0
%283W%5E2-12W%29%2B%285W-20%29=0
3W%28W-4%29%2B5%28W-4%29=0
%28W+-+4%29+%283+W+%2B+5%29+=+0

solutions:
if %28W+-+4%29++=+0=>W=4
if +%283+W+%2B+5%29+=+0=>3W=-5=>W=-5%2F3-> disregard negative solution for the width

now find the length
L=3W-7 ........eq.1
L=3%2A4-7
L=5
so, L=5cm and W=4cm