Wrong Answer From Calculator for x^2-1 (all over) x+4

[alliecr]

I am not getting the answer that my calculator is giving me for the following:

Find the following values for x^2-1 (all over) x+4

f(2a-1)

I am getting 4a^2 (all over) 2a+3 for my final answer and my calculator is getting (2a-1)^2-1 (all over) 2a+3.

What did I do wrong? Also, how do you work the math latex references?
these:
[x[2]^{}[/tex]-1]\frac{}{}[/x+4]

 

[Hydrargyrum]

funny. I got x-4+(15)/(x+4)

 

[HallsofIvy]

funny. I got x-4+(15)/(x+4)

Since the answer must have "a" rather that "x" that's not particularly funny!

I am not getting the answer that my calculator is giving me for the following:

Find the following values for x^2-1 (all over) x+4

f(2a-1)

I am getting 4a^2 (all over) 2a+3 for my final answer and my calculator is getting (2a-1)^2-1 (all over) 2a+3.

Okay, if x= 2a- 1, then x²= (2a-1)²= 4a²- 4a+ 1 so x²- 1= 4a²- 4a. How did you get "4a²"? Also x+ 4= (2a-1)+ 4= 2a+ 3. You have
$$\frac{4a^2- 4a+ 1}{2a+ 3}[/ite]<br /> <br /> <blockquote data-attributes="" data-quote="" data-source="" class="bbCodeBlock bbCodeBlock--expandable bbCodeBlock--quote js-expandWatch"> <div class="bbCodeBlock-content"> <div class="bbCodeBlock-expandContent js-expandContent "> What did I do wrong? Also, how do you work the math latex references?<br /> these:<br /> [x[2]^{} </div> </div> </blockquote>$$

-1]\frac{}{}[/x+4]

The [/tex] only ends a latex code. You need $$in front. Did you know that you can see the code for a latex formula by clicking on it?$$

 

[alliecr]

Since the answer must have "a" rather that "x" that's not particularly funny!


Okay, if x= 2a- 1, then x²= (2a-1)²= 4a²- 4a+ 1 so x²- 1= 4a²- 4a. How did you get "4a²"? Also x+ 4= (2a-1)+ 4= 2a+ 3. You have
$$\frac{4a^2- 4a+ 1}{2a+ 3}[/ite]<br /> <br /> <br /> The$$ only ends a latex code. You need $$in front. Did you know that you can see the code for a latex formula by clicking on it?$$

[tex] <br /> Where does the+1 come from? I had this before I got my answer: $$4a^{2}-2a-2a+1-1...the ones would cancel out right?$$[/tex]

 

[Diffy]

$$f(x) = \frac{x^2-1}{x+4}$$
If x = 2a - 1 then we have:
$$f(2a-1) = \frac{(2a-1)^2-1}{(2a-1) + 4} = \frac{(4a^2 - 4a +1) -1}{2a +3} = \frac{4a^2 - 4a}{2a +3}$$

You could end here or factor out the 4a on the numerator if you really wanted to.
$$\frac{4a(a - 1)}{2a+3}$$

 

[HallsofIvy]

Where does the+1 come from? I had this before I got my answer: $$4a^{2}-2a-2a+1-1...the ones would cancel out right?$$

$$Yes, and I showed that it did. I said (2a-1)²= 4a²- 4a+ 1 so (2a-1)²+ 1= 4a²- 4a just as you have now and just as I had before. But 4a²- 4a is NOT the 4a² you had before!$$