(m-3)(m+3)
(c-7)(c+7)
(4+5a)(5a-4)

^2-это в квадрате1.m^2+3m-3m-9=0m^2-9=0m^2=9m=+-32.с^2+7c-7c-49=0c^2-49=0c^2=49c=+-73.20a-16+25a^2-20a=0-16+25a^2=025a^2=16a^2=25/16a=5/4