# foil doesn't work

• Feb 5th 2009, 06:26 PM
coco
foil doesn't work
solve for x

x^2 - x -26 = 0
• Feb 5th 2009, 06:36 PM
wytiaz
options
$x^2 - x - 26 = 0$

$(x^2 - x ) = 26$

$(x^2 - x +1/4) = 26 + 1/4$

$(x - 1/2)^2 = 105/4$

$x - 1/2 = +or- \sqrt{105}/2$

$x = 1/2 +or- \sqrt{105}/2$
• Feb 5th 2009, 06:41 PM
coco
why do you add 1/4 ??

thanks
• Feb 5th 2009, 06:43 PM
TKHunny
"foil doesn't work"

I am DELIGHTED to see such a thing in writing!!!

Please forget that youever heard the term or used the "method". If you simply learn to multiply, just like multiplying numbers, you do not need this unfortunately obstructive "method" for ANYTHING.

If you need to factor something, please learn to Complete the Square, as demonstrated above, or memorize the Quadratic Formula. These are useful methods.
• Feb 5th 2009, 06:59 PM
Mathnasium
Or it's possible that the FOIL method is a useful method (when it works) and should not be forgotten, since everyone learns differently. FOIL is an excellent method and, with practice, more efficient than either completing the square or the quadratic formula. To discount it because it doesn't work for YOU seems somewhat arbitrary.
• Feb 5th 2009, 07:25 PM
TKHunny
Quote:

Originally Posted by Mathnasium
Or it's possible that the FOIL method is a useful method (when it works) and should not be forgotten, since everyone learns differently. FOIL is an excellent method and, with practice, more efficient than either completing the square or the quadratic formula. To discount it because it doesn't work for YOU seems somewhat arbitrary.

You mistake my intent. I am most certainly not being arbitrary. I'm not saying it doesn't work. My claim is that its usage is horribly limited and its tendency in the classroom is to obfuscate rather than to elucidate. I think it should be discarded to the trash heap, moldering with other refuse, such as "cross-multiply".

Are you saying that it really is too difficult to teach or to learn simple multiplication? Are you failing to differentiate this "method" with the process of factoring? Factoring is also of limited usefulness, being applicable to only a small subset of possibly coefficients, but factoring does not confuse more students than it helps, unlike the source of this conversation.

I see I neglected to include my usual closing,

My views. I welcome others'.