SOLUTION: the length of a rectangle is five feet less than twice the width. its area is 375 square feet. Find its dimensions. I need to know how to work it out.. Or just a equation

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Question 692302: the length of a rectangle is five feet less than twice the width. its area is 375 square feet. Find its dimensions. I need to know how to work it out.. Or just a equation
Answer by Stitch(470)   (Show Source): You can put this solution on YOUR website!
Set-Up
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A = L * W (Area of a rectangle)
Given: A = 375, L = 2W - 5
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Solution:
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Substitute the given information into the equation for the area of a rectangle
Simplify
Subtract 128 from both sides

Use the quadratic equation
Solved by pluggable solver: SOLVE quadratic equation with variable
Quadratic equation (in our case ) has the following solutons:



For these solutions to exist, the discriminant should not be a negative number.

First, we need to compute the discriminant : .

Discriminant d=3025 is greater than zero. That means that there are two solutions: .




Quadratic expression can be factored:

Again, the answer is: 15, -12.5. Here's your graph:


The answers were W = 15feet or -12.5feet. but since you can not have a negative width. Just use the 15
Now we can find the length
L = 2W - 5
Plug 15 in for W
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