Question 1138434
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<pre>

{{{(x+9)^2}}} = {{{16x^2}}}    =====>  take square root of both sides  ====>


x + 9 = 4x


9 = 4x - x = 3x


x = 9/3 = 3.


<U>ANSWER</U>.  The original square side length is 3 inches.


<U>CHACK</U>.   {{{(3+9)^2}}} = 144;   {{{16*3^2}}} = 16*9 = 144.    ! Correct !
</pre>

Solved.


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Regarding the post by @Theo and comparing it with my, I notice that in his solution he makes a lot (tons (!) ) unnecessary calculations.