Найдите значение выражения (6m-n)(6m+n)-(12m-5n)(3m+n) при m=-8/9 n=3/4

(6m - n)(6m + n) - (12m - 5n)(3m + n) =
= (6m)² - n² - (36m² + 12mn -15mn -5n²) =
= 36m² - n² - 36m² +3mn + 5n² =
= (36m² - 36m²) + 3mn + (5n² - n²) =
=3mn + 4n² = n*( 3m + 4n )
$m = - \frac{8}{9} ; n= \frac{3}{4} \\ \\ \frac{3}{4} * (3 *(- \frac{8}{9}) + 4 * \frac{3}{4}) = \frac{3}{4} *(- 2\frac{2}{3} + 3)= \frac{3}{4} * \frac{1}{3} = \frac{1}{4} =0.25 \\$