Solve the quadratic expression by completing the square.
x2 + 10x – 17 = 7

I did the problem but when I plug my answers into the original equation it doesn't work. this is what i got.
x^2+10x-24=0
(x+2)(x-12)=0
x=-2,12

Question

Solve the quadratic expression by completing the square.
x2 + 10x – 17 = 7

I did the problem but when I plug my answers into the original equation it doesn't work. this is what i got. 
x^2+10x-24=0
(x+2)(x-12)=0
x=-2,12

anonymous · Answer

You need to change the signs...(x + 2)(x -12) = x^2 - 10x -24!

anonymous · Answer

OHH I see, and wait do I have to use some other method to solve this, since it says to solve by completing the square. I have to show my work so I have to make sure I do the problem the way it says or I will get it wrong.

anonymous · Answer

Good point...you do need to use a different method. See this link: http://www.purplemath.com/modules/sqrquad.htm

hero · Answer

Yes, he should learn how to complete the square because x^2 - 10x - 24 is not even the right polynomial to use.

anonymous · Answer

Can I please get some help on how to do this the right way? I'm confused

anonymous · Answer

I think I probably know how to complete the square, I just need to re-jog my memory a bit

hero · Answer

$$x^2+10x-24=0
\x^2 + 10x = 24
\x^2 + 10x + 25 = 24 + 25
\(x + 5)^2 = 49
\x + 5 = \pm 7
\x = \pm7 - 5
\x = 2
\x = -12$$

hero · Answer

The trick is to remember to get whatever you're working with to the form $ax^2 + bx = c$ Then afterwards, add $\left(\frac{b}{2}\right)^2$ to both sides.

anonymous · Answer

Thanks so much, I get it:)