Final answer to the problem
$y=81x^{6}+126x^{5}+49x^{4}$
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Step-by-step Solution
Specify the solving method
1
Expand the expression $\left(9x^3+7x^2+8\right)^2$ using the square of a binomial: $(a+b)^2=a^2+2ab+b^2$
$y=81x^{6}+126x^{5}+49x^{4}$
Final answer to the problem
$y=81x^{6}+126x^{5}+49x^{4}$