Answers

2016-06-18T15:41:04+08:00
X     =   Let be the length
x-4  =  width

A    =   LW
A     =  x(x-4)
 81   =   x^{2} -4x
Apply Subtraction Property of Equality. Subtract 81 to both sides.
0     =  x^{2} -4x-81
The equation is  x^{2} -4x-81=0, which is a quadratic equation.
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