# Thread: Solving an equation using the quadratic formula and completing the square method

1. ## Solving an equation using the quadratic formula and completing the square method

I used both methods on the same equation, but I got different answers. The one on the left is the quadratic equation while the one on the right is completing the square. Can anyone spot my mistake? Thanks!

2. ## Re: Solving an equation using the quadratic formula and completing the square method

in the quadratic formula version you forget to divide sqrt(-48) by 4

in the completing the square version you divide the 8 by 2 properly but then it shows up again as 8 inside the parens.

slow down and redo both carefully

3. ## Re: Solving an equation using the quadratic formula and completing the square method

Now is it good?

4. ## Re: Solving an equation using the quadratic formula and completing the square method

Your Quadratic Formula is correct. Your completing the square is not. When you square root both sides, you have to square root the 2 as well, or divide by 2 first.

5. ## Re: Solving an equation using the quadratic formula and completing the square method

Thanx .. .. Relay u post is so valuable & very informative Sir ..

6. ## Re: Solving an equation using the quadratic formula and completing the square method

I did what u asked me to do... Here's my new answer

7. ## Re: Solving an equation using the quadratic formula and completing the square method

Sorry ! I don't understand u ans .. ..

looks good

9. ## Re: Solving an equation using the quadratic formula and completing the square method

No it doesn't.

\displaystyle \begin{align*} 2 \left( x^2 + 2x + 1 - 1 + 4 \right) &= 2 \left[ \left( x + 1 \right) ^2 + 3 \right] \\ &= 2\left( x + 1 \right) ^2 + 6 \end{align*}

not \displaystyle \begin{align*} 2 \left( x + 1 \right) ^2 + 3 \end{align*}

10. ## Re: Solving an equation using the quadratic formula and completing the square method

Thank's .. ..