Quote:Original post by Zanshibumi
-x-x = 0;
No, that is only the case when x=0. -x-x = -2x.
Quote: (-x-x) squared would be ?
2x squared?
Instead of trying to remember a lot of complicated rules try to consider what you're doing. - x - x must equal -2x, which is a product of two numbers (-2 and x). When squaring a product we can just square its factors separately like so:
(-2x)2 =
(-2)2x2 =
4x2
Remember that when we say 2x we just mean 2 times x. Try to think about what you're doing instead of remembing rules for all kind of stuff. For instance if you've got:
(x+2)2
How would you expand it? Squaring is simply a multiplication by itself so we have:
(x+2)(x+2)
To simplify it a little we introduce another identifier, y which we makes equal to (x+2), then we have:
(x+2)y
We then multiply into the parantheses:
xy+2y
We then expand the y to what it actually stood for:
x(x+2)+2(x+2)
We then multiply into the parantheses again:
xx+2x+2x+2*2
Since 2x+2x=4x, 2*2=4 and xx=x2 we get:
x2+4x+4
Simple if you just give it a little thought and know your basic rules. Also you don't really need to introduce the extra identifier y, but I felt it would help show how you can multiply into parantheses even when you multiply by a sum.
