# No idea how to do this

• May 8th 2008, 02:16 PM
lax600
No idea how to do this
\$\displaystyle (x - y)^2 + 13(x - y) + 42\$

Please someone help me or something. I have no idea how to do this at all.
Like what do I do when its \$\displaystyle (x - y)^2\$?
• May 8th 2008, 02:30 PM
icemanfan
Quote:

Originally Posted by lax600
\$\displaystyle (x - y)^2 + 13(x - y) + 42\$

Please someone help me or something. I have no idea how to do this at all.
Like what do I do when its \$\displaystyle (x - y)^2\$?

I'm guessing you want to expand this.

\$\displaystyle (x - y)^2 = x^2 - 2xy + y^2\$, for starters.
• May 8th 2008, 02:31 PM
lax600
I need to factor it... so I still expand it?
• May 8th 2008, 02:34 PM
icemanfan
\$\displaystyle (x - y)^2 + 13(x - y) + 42\$ is about as factored as it gets. One thing you can do:

\$\displaystyle (x - y + 13)(x - y) + 42\$
• May 8th 2008, 02:51 PM
lax600

\$\displaystyle (x - y)^2 - 13(x - y) + 42\$

if \$\displaystyle (x - y)^2 - 14(x - y) + 49\$

\$\displaystyle (x - y)^2 - 2*7*(x - y) + 7^2\$

a =\$\displaystyle (x - y)^2\$
b =\$\displaystyle 7\$

\$\displaystyle (x - y)^2 - 13(x - y) + 42
= [(x - y)^2 - 14(x - y) + 49]
={[(x - y) - 7]^2 + [(x - y) - 7]}\$
\$\displaystyle =(x - y -7){x - y - 7}
=(x - y - 7)(x - y - 6)\$
• May 8th 2008, 02:58 PM
icemanfan
Quote:

Originally Posted by lax600

\$\displaystyle (x - y)^2 - 13(x - y) + 42\$

if \$\displaystyle (x - y)^2 - 14(x - y) + 49\$

\$\displaystyle (x - y)^2 - 2*7*(x - y) + 7^2\$

a =\$\displaystyle (x - y)^2\$
b =\$\displaystyle 7\$

\$\displaystyle (x - y)^2 - 13(x - y) + 42
= [(x - y)^2 - 14(x - y) + 49]
={[(x - y) - 7]^2 + [(x - y) - 7]}\$
\$\displaystyle =(x - y -7){x - y - 7}
=(x - y - 7)(x - y - 6)\$

yeah, that's right. Just substitute \$\displaystyle t = x-y\$ and you have \$\displaystyle t^2 - 13t + 42\$ which easily factors to \$\displaystyle (t - 6)(t - 7)\$. I should have been thinking along those lines.
• May 8th 2008, 03:01 PM
lax600
oh