[tex]\displaystyle\bf\\7)\\a)\\-5x^2=-180\\\\x^2=\frac{-180}{-5}=\frac{180}{5}=36\\\\x=\pm\sqrt{36}=\pm6\\\\x_1=-6\\\\x_2=6\\\\b)\\-36x^2=-225\\\\x^2=\frac{-225}{-36}=\frac{225}{36}\\\\x=\pm\sqrt{\frac{225}{36}}=\pm \frac{15}{6}=\pm \frac{5}{2}\\\\x_1=-\frac{5}{2}\\\\x_2=\frac{5}{2}[/tex]
