Solving an equation using the quadratic formula and completing the square method

• Feb 15th 2014, 07:53 PM
asilvester635
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!
• Feb 15th 2014, 08:36 PM
romsek
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
• Feb 16th 2014, 07:55 PM
asilvester635
Re: Solving an equation using the quadratic formula and completing the square method
Now is it good?
• Feb 16th 2014, 08:32 PM
Prove It
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.
• Feb 17th 2014, 06:29 AM
joo003464
Re: Solving an equation using the quadratic formula and completing the square method
Thanx .. .. Relay u post is so valuable & very informative Sir .. ;) ;) ;)
• Feb 17th 2014, 09:53 AM
asilvester635
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
• Feb 18th 2014, 11:26 PM
joo003464
Re: Solving an equation using the quadratic formula and completing the square method
Sorry ! I don't understand u ans .. ..
• Feb 19th 2014, 12:02 AM
romsek
Re: Solving an equation using the quadratic formula and completing the square method
looks good
• Feb 19th 2014, 12:06 AM
Prove It
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*}
• Feb 19th 2014, 12:58 AM
joo003464
Re: Solving an equation using the quadratic formula and completing the square method
Thank's .. .. ;) ;) ;)