Question 999628
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First, find the pyramids base area.

For it, use the given volume and the height.


Since V = {{{(B*h)/3}}}, you have B = {{{(3*V)/h}}} = {{{(3*252)/12}}} = 63 {{{cm^2}}}. 


Now, for the length of the shorter edge of the base you have an equation


x*(x+2) = 63.


Solve this quadratic equation, using the quadratic formula, or the Viete's theorem, or factorization method.


The solution is x = 7 cm.