Function Question URGENT HELP needed.

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MooreC1

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Apr 8, 2005
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The directions say that "For each function, find f(3), f(-2), and f(a-b).

the problem is f(x)=5x+3.

I tried this problem and when f(3) the answer I got was 18.

when f(-2) I got -7, and when f(a-b) I got 3.

Are these correct??

If not, show me what's wrong and how to fix them.

I also have a couple more of these problems that look confusing to me but I'll post those later :mrgreen:
 
MooreC1 said:
f(x)=5x+3.
Click to expand...
f(a-b) = 5*(a-b) + 3
The only way to get '3' is to have a = b. That is not given in the problem statement. How did you get '3'?
 
Like I said I'm very confused and I obviously don't know what i'm doing. Help me solve the problem f(x)=5x+3 when f(3), f(-2), & f(a-b). Please!!
 
Since you did the first two correctly, and I just did the last one, what kind of additional help do you have in mind?

How did you get f(a-b) = 3??? The answer to this question may reveal your last misunderstanding and you'll be on your way. Maybe not.
 
Heres what I did.

f(x)=5x+3
f(x)=5(a-b)+3
f(x)=5a-5b+3
f(x)=3

I don't know what i'm doing wrong here, help!!
 
FUNCTION NOTATION:
If f(x)=5x+3 then f(y)=5y+3; f(a)=5a+3; f(−a)=5(−a)+3=−5a+3.
Also, f(a−b)=5(a−b)+3=5a−5b+3.

If g(x)=x<SUP>2</SUP>−3x+5 then g(a)=a<SUP>2</SUP>−3a+5 and g(−a)= (−a)<SUP>2</SUP>−3(−a)+5=a<SUP>2</SUP>+3a+5 and g(4x)=16x<SUP>2</SUP>−12x+5.
 
Can you help me with my problem??
Click to expand...

Hi, MooreC1,

TK and PKA are showing you everything you need. Please study their responses carefully.

You handled the function notation just fine when you were given numbers rather than variables. TK and PKA are showing you that variables work the same way as actual numbers.

I'm guessing that your only confusion occurred when you were given TWO variables at once, as in "a-b".

f(x)=5x+3
f(x)=5(a-b)+3
f(x)=5a-5b+3
f(x)=3
Click to expand...

You did great until the last step. 5a - 5b does not equal 0, because a and b are not necessarily the same number. You should have stopped at the third step:

f(a-b) = 5a - 5b + 3

Hope that helps.
 
yep that makes me understand that problem, now i just came across same type of problem that has fractions.

f(x)=1/2-x

when x is 3 i get -1, when x is -2 i get .25.

when x is a-b I get to f(a-b)= 1/2-(a-b), what do I do next??
 
when x is a-b I get to f(a-b)= 1/2-(a-b), what do I do next??
Click to expand...

You can pretty much stop there -- or you can get rid of the parentheses around "a-b" by distributing the "-":

f(a-b)= 1/2-(a-b) = 1/(2-a+b)

PS Notice I put parentheses around the entire denominator. It's important you do that to make clear what's in the denominator and what's not.
 
I got 1 more for ya.

note: ! equals vertical lines

f(x)=!2x-5!

x is 3 I get !1!, x is -2 i get !-9! are these correct??
when x is a-b I get:
f(a-b)=!2a-2b-5!
 
To type the vertical line, use the "pipe" character, which is probably somewhere above your "Enter" key. (It may look like a broken line, but it'll type solid.)

To learn what the "vertical lines" notation means, review this lesson. Then you'll know how to finish f(3) and f(-2).

Eliz.
 
“! equals vertical lines” that is of course absolute value, the distance the number is from 0.
So |1|=1 and |−9|=9 because −9 is 9 units from 0.
Yes f(a−b)=|2a−2b−5|.
 
I like to ask, "What's 3 dogs minus 4 cats?" Well? :)

You can't subtract cats from dogs, can you?

5a - 5b is similar. b and a don't mix unless you know more about them. 5a - 5b is all you get. Nothing else to do.
 
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