Can someone please explain this to me? (Hard Math Question)

[scrivener]

<p>This question is making me angry. I'm mainly having trouble understanding where to plug in all of the values... Please help! :P</p>

<p>Let (x)* be defined as (x)=x^2 - x for all values of x. If (a)=(a-2), what is the value of a?
* in this problem, the parentheses are circles around the values, so those x's and a's really are encircled.</p>

<p>I found this as an explanation from yahoo answers:
a² - a = [a-2]² - [a-2]
a² - a = a^2 - 4a + 4 - a + 2
a² - a = a² - 5a + 6
Subtract a² from both sides:
-a = -5a + 6
Add 5a to both sides:
4a = 6
Divide both sides by 4:
a = 3/2</p>

<p>I understand everything past the first line, but why is the first line set up like that? Thanks!</p>

[RickyRich]

<p>The circle around any number, in this case a and a-2 represent a function given by (x)=x^2-x. Since this function to a is equal to this function to a-2, or basically (a)=(a-2) as you put it, you have to apply the function of the circle to both sides. Therefore, the left side becomes a^2-a, and the right side becomes (a-2)^2 - (a-2).
Hope this helps!</p>

[scrivener]

<p>Yup, I got it now thanks</p>