Question 1091359
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The missed term is {{{(-81/16)*x^2}}}.


Indeed, {{{9x - ((-81/16)*x^2) + 4}}} = {{{(81/16)x^2 +9x + 4}}} = {{{((9/4)*x)^2 + 2*((9/4)*x)*2 + 4}}} = {{{((9/4)x+2)^2}}}.
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Solved.