-1(x-8)=8x-81
-x^2+8x-8x=-81
-x^2=-81
x^2=81
x1=+9 x2=-9
(5x-2y)^2=25х^2-2*5x*2y+4y^2=<em><u>25x^2-20xy+4y^2</u></em>