-5a²-ab-5b-5a²+4ab= -10a²+3ab-5b
-10*9-3*3*2+5*2= -90-18+10= -98
1)(x-2)*(2x+1)
2)(x+3)*(3x-1)
3)(x+1)*(3x-1)
4)(x+3)*(2x-1)
5)(x-6)*(x+5)
6)(x-6)*(x+7)
7)(x+4)*(2x-1)
8)(x-1)*(5x+2)
9)(x+1)*(3x+2)
10)(x-2)*(2x-3)
пусть n=5, тогда, х5= (5+2) / (5^2-4)
x5= 7/21 = 1/3