Question

25(a) в квадрате – 81 = 0.

Answer 1

$25a^2-81=0 \\ (5a-9)(5a+9)=0 \\ \left[\begin{array}{ccc}5a-9=0\\5a+9=0\end{array}\right\to \left[\begin{array}{ccc}a_1=1.8\\a_2=-1.8\end{array}\right$