# Factoring

• Sep 22nd 2012, 08:04 PM
sakonpure6
Factoring
I have this advanced grade 11 factoring question $y^4+2y^2+9$ and i know the answer is $(y^2+3-2y)(y^2+3-2y)$ however I do not know how to get there because when i first factored it i got $y^2(y+1)(y-1)+9$ which is wrong. Any help or tricks are appreciated!

• Sep 22nd 2012, 08:15 PM
MarkFL
Re: Factoring
$y^2+2y^2+9=3y^2+9=3(y^2+3)$
• Sep 22nd 2012, 08:17 PM
sakonpure6
Re: Factoring
sorry i wrote down the wrong question.
• Sep 22nd 2012, 10:49 PM
Soroban
Re: Factoring
Hello, sakonpure6!

The answer you gave is wrong . . .

Quote:

$\text{Factor: }\:y^4+2y^2+9$

We have: . $y^4 + 9 + 2y^2$

Add and subtract $6y^2:$

. . $y^4 {\color{red}\:+\: 6y^2} + 9 + 2y^2 {\color{red}\:-\: 6y^2} \;=\;(y^4 + 6y^2 + 9) - 4y^2$

. . . . . $=\;(y^2+ 3)^2 - (2y)^2$ . . . a difference of squares!

Factor: . $\big[(y^2+3) - 2y\big]\,\big[(y^2+3) + 2y\big] \;=\;(y^2 - 2y + 3)(y^2 + 2y +3)$
• Sep 23rd 2012, 10:42 AM
sakonpure6
Re: Factoring
why did you choose to add 6y^2? can it be something else as long as we get a perfect square trinomial or...?
• Sep 23rd 2012, 09:16 PM
manoj9585
Re: Factoring
it's a algebra solving trick, I learn it in my 12th grade, where I learnt more techniques and procedures of trigonometry and other problem solving phenomenon. Most of problem and Solving Linear Equations With Fractions are also solved by using adding and subtracting.
• Sep 24th 2012, 01:09 PM
sakonpure6
Re: Factoring
thank you but i still do not understand how Soroban came up with $6y^2$ to add and subtract