1. ## Completing the square

Confused how you get from step 1 to step 2

I don't understand how you get the -7 from x^2-2x

2. This looks like you picked up the algebra in the middle of a problem. Could you please state the original problem? Thanks!

3. Solve x2 = 2x + 7 (a similar equation to the earlier example)

First rearrange to get: x2 - 2x − 7 = 0

Rough Working for the solution:

4. Ok. That makes more sense now. Your first step is fine, although I would probably leave the 7 on the RHS. Different people complete the square in different ways.

$\displaystyle x^{2}-2x=7$. I pulled the 2x over to the LHS.
$\displaystyle x^{2}-2x+1=7+1$. I added the square of half the coefficient of the x term to both sides. Then you get
$\displaystyle (x-1)^{2}=8$. From here, it looks as though you've solved the rest of the problem.

5. Originally Posted by Ackbeet
Ok. That makes more sense now. Your first step is fine, although I would probably leave the 7 on the RHS. Different people complete the square in different ways.

$\displaystyle x^{2}-2x=7$. I pulled the 2x over to the LHS.
$\displaystyle x^{2}-2x+1=7+1$. I added the square of half the coefficient of the x term to both sides. Then you get
$\displaystyle (x-1)^{2}=8$. From here, it looks as though you've solved the rest of the problem.
thanks, you're explanation is much better

6. You're welcome. Have fun!