[tex]\displaystyle 1)\frac{x^2}{x-9}=\frac{81}{x-9},x\neq 9\\ \\x^2=81\\x=б9\\x=-9\\\\2)x^4-5x^2-36=0\\t^2-5t-36=0\\t=-4,t=9\\x^2=-4,x^2=9\\x \notin, x=-3, x=3\\x=б3[/tex]