Function Notation: f(x+4)=2x(squared)+3x-1

[Kathleen bell]

Already school has just started and I'm stuck. I understand part of it, but not all of it. I know how to plug things in but I can't seem to get the right answer. I'm in Pre-calc and it's a college level course and my high school is really behind in it's way of teaching. So, it's kind of a shock to the system because this year we're moving really fast. Up to three sections of a chapter per day.

ANYWAY, my problem is I have the answer, but I'm not sure how the book arrives at it. The problem is:

f(x+4)=2x(squared)+3x-1

and the answer is:

2x(squared)+19x-1

I know that you plug in x+4 into every area that x is located and I've tried both multiplying and squaring first to see if that would find the correct answer. This is where I normally get stuck:

2(x=4)(squared)+3(x+4)-1

I know that you do parenthases first in order of operations and than exponents, but when I try that, I still can't get the 19x in the middle. Please help me.

 

[tkhunny]

Re: Function Notation

f(x+4)=2x(squared)+3x-1

Are you SURE you mean that? Perhaps it was this:

f(x) = 2x^2 + 3x - 1
Find f(x+4)

Something like that?

If so, f(x+4) = 2(x+4)^2 + 3(x+4) - 1
= 2(x^2 + 8x + 14) + 3x + 12 - 1
= 2x^2 + 16x + 28 + 3x + 12 - 1
= oh, you finish.

I don't like the answer you gave. At least, it doesn't seem to match the problem I made up.

 

[Kathleen bell]

Re: Function Notation

f(x+4)=2x(squared)+3x-1

Are you SURE you mean that? Perhaps it was this:

f(x) = 2x^2 + 3x - 1
Find f(x+4)

Something like that?

If so, f(x+4) = 2(x+4)^2 + 3(x+4) - 1
= 2(x^2 + 8x + 14) + 3x + 12 - 1
= 2x^2 + 16x + 28 + 3x + 12 - 1
= oh, you finish.

I don't like the answer you gave. At least, it doesn't seem to match the problem I made up.

Yes! That's it! Thank you so much! I forgot to do the carrot thing.... Sorry, I blanked out. Which answer? Where I was plugging things in or the answer I said I had? The answer came directly from the book, which is what makes me mad, cause I didn't like it either.

 

[tkhunny]

You do have to learn to rely on yourself. Books have incorrect answers. Count on it.