y^2 -2y = 17
(y - 1)^2 -1 = 17
(y -1)^2 = 18
y - 1 = +/- sqrt 18
y = 1 +/- 3 sqrt 2
This one can be solved by factoring.
6y^2 - 5y - 4 = 0
(3y - 4)(2y + 1) = 0
Expanding this using FOIL might help you to understand how I factored.
Set each factor to 0 and solve for y.
3y - 4 = 0
3y = 4
y = 4/3
and
2y + 1 = 0
2y = -1
y = - 1/2
Do you understand that?