The teacher will be very surprised to see your correct solution 😉
a*x^2 + b*x + c = 0
D = b^2 - 4 * a * c =
(2)^2 - 4 * (1) * (26 + y^2 - 10*y) = -100 - 4*y^2 + 40*y
x1 = (-b + sqrt(D)) / (2*a)
x2 = (-b - sqrt(D)) / (2*a)
x1 = -1 + I*(5 - y)
x2 = -1 + I*(-5 + y)
sum
0 + -1 + I*(5 - y) + -1 + I*(-5 + y)
=
-2 + I*(-5 + y) + I*(5 - y)
product
1*(-1 + I*(5 - y))*(-1 + I*(-5 + y))
=
2 26 + y - 10*y
26 + y^2 - 10*y