А) X^2-8x-9=0 б) x^2-17x+42=0 в) у^2+8y+15=0 г) z^2-3z-10=0 д) y^2-11y-80=0

1)x - 8x - 9 = 0 ;
x + x - 9x - 9 = 0 ;
x (x + 1)- 9 (x + 1)= 0 ;
(x + 1)(x - 9)= 0 ;
x + 1 = 0 ;
x - 9 = 0 ;
x = -1 ;
x = 9 .
2)x - 17x + 42 = 0 ;
x - 3x - 14x + 42 = 0 ;
x (x - 3)- 14 (x - 3)= 0 ;
(x - 3)(x - 14)= 0 ;
x - 3 = 0 ;
x - 14 = 0 ;
x = 3 ;
x = 14 .
3)y + 8y + 15 = 0 ;
y + 5y + 3y + 15 = 0 ;
y (y + 5) + 3(y + 5)= 0 ;
(y + 5)(y + 3)= 0 ;
y + 5 = 0 ;
y + 3 = 0 ;
y = -5 ;
y = -3 .
4)z - 3z - 10 = 0 ;
z + 2z - 5z - 10 = 0 ;
z (z + 2)- 5 (z + 2)= 0 ;
(z + 2)(z - 5)= 0 ;
z + 2 = 0 ;
z - 5 = 0 ;
z = -2 ;
z = 5 .
5)y - 11y - 80 = 0 ;
y - 5y - 16y - 80 = 0 ;
y (y + 5)- 16 (y + 5)= 0 ;
(y + 5)(y - 16)= 0 ;
y + 5 = 0 ;
y - 16 = 0 ;
y = - 5 ;
y = 16 .