# Re: mom needs help

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Posted by T.Gracken on October 14, 2002 at 11:19:35:

In Reply to: mom needs help posted by Pat on October 14, 2002 at 00:25:10:

: I'm trying to relearn algebra so I can be of some help to my son! I don't want to just have an answer to a problem for him, I want to help him understand how it works. I was a wiz when I was in class, but the memory of how to do this has faded with time!

: What am I looking for on the math sites to help me figure this type of problem?

: f(x)= 4x + 7 and g(x) = 2x + 8...find f(2)

: pw

when equations are written using f(x), g(x), "something"(x), it is simply a way that mathematicians label equations. That is, instead of saying

suppose we let equation 1 be y = 4x + 7 and equation 2 be y = 2x + 8 (and so on).

we just call equation one f. and y = f(x) [read: why equals eff ov ex] Also, equation 2 we will call g and y = g(x) here [read: why equals jee ov ex]

This notation is used for a number of reasons. One being laziness. Instead of me asking, "what is the y value for equation 1 when we replace the x with the number 2?", I can simply write find f(2) and I have said the same thing. But I don't even have to go back and label equations and such.

So f(2) means "what is 4x+7 equal to when the x is replaced with 2?"

i.e. f(2)=15.

other examples:

what is g(1)? ...that is what is 2x+8 equal to when x is replaced with 1? [I know to use 2x+8 since g(x)=2x+8 and the problem references "g"]
so, g(1)=10.

hope that helps

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