Thread: Solve by factoring/completing the square

If you can't solve by factoring, solve by completing the square.

27. y^2 - 2y = 17



I can't remember how to solve by completing the square. If someone could help with this one, I should be able to remember.

y^2 -2y = 17

(y - 1)^2 -1 = 17

(y -1)^2 = 18

y - 1 = +/- sqrt 18

y = 1 +/- 3 sqrt 2

Okay, so I still don't understand how you knew to do that exactly. And I'm pretty sure we didn't do this in class...I don't remember this at all.

6y^2 - 5y = 4

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?

Yeah, I do, I didn't realize it could be factored. Thanks.