Length of Side of Square

If the numerical value of the area of a square plus two times the numerical value of its perimeter is equal to 20, what is the length of one side of the square?
Source: NCTM Mathematics Teacher, September 2006

Solution
Let a represent the length of one side of a square. The following equation is true
a^2+2(4a)=20
a^2+8a-20=0
(a-2)(a+10)=0
a=2 or a=-10 (extraneous solution)
The length of one side of the square equals 2 units.

Answer: 2 units

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About mvtrinh

Retired high school math teacher.
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