Tyrion101 said:
Right now I am working on complex fractions, and have been trying all day to factor them, the way it worked in the previous lessons, and, it's not working. I'm working on fraction a + fraction b divided by fraction c - fraction d, and nothing seems to give me a right answer. It's driving me nuts, because, as I said, I've been doing it the same way all along and now it's not working, and I can't figure out why. I tried giving an example earlier, but it got axed for being a homework type question.
I saw what you posted - why don't you try posting it in the Precalc section under Homework and Coursework?
One problem is that you weren't factoring the complex fractions - you were actually supposed to simplify them, which could mean that you need to factor the numerator or denominator or both. However, whatever you learned before should still be valid, whether you're working with fractions made up of numbers or fractions made up of algebraic expressions. The same ideas apply to both.
A mistake that beginning students make often is cancelling when they shouldn't do so. What cancelling really is, is finding
factors that are the same in the numerator and denominator, and getting rid of them. An important word here is
factor, which implies two expressions that are multiplied.
For example, this is incorrect:
$$ \frac{10 + 8 }{5 + 4} = 2 + 2 = 4$$
This is actually 18/9, which is nowhere near 4.
And this is correct.
$$ \frac{10 + 8}{5 + 4} = \frac{18}{9} = \frac{2 * 9}{9} = \frac{2}{1} * \frac{9}{9}= 2$$
9 is a factor in the numerator and denominator, which means the whole fraction can be thought of as having a factor of 1. Multiplication by 1 always leaves you with exactly the same value.
Things work the same way with variables, except you need to be careful of factors in the denominator that could be zero.