Question

(2m-3n-4)*(4m*m+9n*n+6mn-12n+8m+16)​

Answer 1

Assume entire expression as x and then square it..

$\sf \color{blue}You'll \: get \: an \: equation \: x^2 =3+x</p><p>$

$\color{red} \sf \: Then \: solve \: the \: quadratic \: equation x^2-x-3=0$

X=( 1+√13) /2 which is the answer for your question.