Question 844440
ORIGINAL


y length, x width
{{{y=3x}}}
A for area, {{{A=xy}}}, {{{A=x*3x}}}, {{{A=3x^2}}}


CHANGED


Length becomes y+3, and width becomes x-1;
The changed rectangle area, {{{(x-1)(y+3)=72}}}.

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{{{xy-y+3x-3=72}}}
The analysis in "Original" shows that xy=A=3x^2, so we can substitute that here.
{{{3x^2-y+3x-3=72}}}
The analysis in "Original" also shows that y=3x, so we can substitute for y.
{{{3x^2-3x+3x-3=72}}}, extremely neat since the changed equation already contains a 3x term.
{{{3x^2-3x+3x-3+3=72+3}}}
{{{3x^2+3x-3x=75}}}
{{{3x^2=75}}}
{{{x^2=75/3=25}}}
{{{highlight(x=5)}}}-------Width of the original rectangle.
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{{{y=3x=3*5=15}}}; {{{highlight(y=15)}}}-------Length of original rectangle.