а)b^2c-9c=с (b²-9) =c (b-3) (b+3)
б)2a^2+12a+18=2 (a²+6a+9) =2 (a+3)²
в)x-y-2x^2+2y^2=x-y-2 (x²-y²) =x-y-2 (x-y) (X+y) = (x-y) (-2 (x+y) +1) = (x-y) (-2x-2y+1)
