# Plugging in x and y.... really simple stuff but I'm having trouble

• Nov 16th 2012, 08:25 PM
asilvester635
Plugging in x and y.... really simple stuff but I'm having trouble
Heres the equation to which where you'll need to plug in x and y
(-2y)(-2x) - [1 -2x -2y]

plug these in the equation given above... (x=1/3, y=1/3)
the answer is 1/3 but idk how the book got that answer...

here what I have so far after plugging in the x and y into the equation...
= (-2/3)(-2/3) - [1 - 2/3 - 2/3]
= 4/9 - [1 - 4/3]..... IM STUCK HERE..... did i do anything wrong??
• Nov 16th 2012, 09:06 PM
chiro
Re: Plugging in x and y.... really simple stuff but I'm having trouble
Hey asilvester635.

You did everything right as long as you evaluate the expression correctly as you have it.
• Nov 16th 2012, 09:11 PM
asilvester635
Re: Plugging in x and y.... really simple stuff but I'm having trouble
So this is what i got next

= 4/9 - [1/1 - 4/3]
= 4/9 - [3/3 - 4/3]
= 4/9 - [-1/3]
= 4/9 + 1/3
= 4/9 + 3/9
= 7/9

Why didn't i get 1/3 as my answer? did i do anything wrong now?
• Nov 16th 2012, 09:24 PM
asilvester635
Re: Plugging in x and y.... really simple stuff but I'm having trouble
So this is what i got next

= 4/9 - [1/1 - 4/3]
= 4/9 - [3/3 - 4/3]
= 4/9 - [-1/3]
= 4/9 + 1/3
= 4/9 + 3/9
= 7/9

Why didn't i get 1/3 as my answer? did i do anything wrong now?
• Nov 16th 2012, 09:34 PM
chiro
Re: Plugging in x and y.... really simple stuff but I'm having trouble
Using R, (so there is no ambiguity) I plug that in and get:

> (-2/3)*(-2/3) - (1 - 2/3 - 2/3)
[1] 0.7777778
> 7/9
[1] 0.7777778

This matches youe answer of 7/9 and not an alternative.
• Nov 17th 2012, 12:07 PM
asilvester635
Re: Plugging in x and y.... really simple stuff but I'm having trouble
oops sorry i forgot to add an exponent of 2 at the end of [1 -2x -2y]... but thanks if figured it out.