Answer:
The length is 15 yards
Step-by-step explanation:
Given
Represent the width with W and length with L: So
[tex]Area = 135yd^2[/tex]
[tex]L=3W - 12[/tex]
Required
Determine the length of the rectangle:
Area is calculated as thus:
[tex]Area = L * W[/tex]
Substitute 3W - 12 for L and 135 for Area
[tex]135= (3W - 12) * W[/tex]
[tex]135= 3W^2 - 12W[/tex]
Reorder:
[tex]3W^2 - 12W - 135= 0[/tex]
Divide through by 3
[tex]W^2 - 4W - 45 = 0[/tex]
Expand:
[tex]W^2 - 9W + 5W - 45 = 0[/tex]
[tex]W(W - 9) + 5(W - 9) = 0[/tex]
[tex](W + 5)(W-9) = 0[/tex]
[tex]W + 5 = 0[/tex] or [tex]W - 9 = 0[/tex]
[tex]W = -5[/tex] or [tex]W = 9[/tex]
But width can't be negative
So:
[tex]W = 9[/tex]
Recall that: [tex]L=3W - 12[/tex]
[tex]L = 3 * 9 - 12[/tex]
[tex]L = 15[/tex]
Hence, the length 15 yards
