Discussion about math, puzzles, games and fun. Useful symbols: ÷ × ½ √ ∞ ≠ ≤ ≥ ≈ ⇒ ± ∈ Δ θ ∴ ∑ ∫ π -¹ ² ³ °

You are not logged in.

- Topics: Active | Unanswered

Pages: **1**

**skylor blay****Guest**

I have to find the domain, vertical and horizontal asymptotes, and the y-intercept and graph it for.

f(x) 3x^2 + 4/x^2-x-6 and

g(x) = 2x-15/x^2-8x+15

I was marked 4/8 but wasn't told what I did wrong.

**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 83,138

Hi;

Says there you also have to graph it. Did you go here and do that?

**In mathematics, you don't understand things. You just get used to them.I have the result, but I do not yet know how to get it.All physicists, and a good many quite respectable mathematicians are contemptuous about proof.**

Offline

**skylor****Guest**

I believe my graph is correct. I will try it out.

**skylor****Guest**

I'm also pretty sure both of the asymptotes are correct, not so sure about the domain and y intercept. The graph is also kind of sloppy.

**bob bundy****Moderator**- Registered: 2010-06-20
- Posts: 6,269

hi Skylor,

I'm assuming that is

when x = 0

The vertical asymptotes are at x = -2 and x = + 3.

I'm never happy with these questions that ask for the domain. I think the setter should be declaring a domain as part of the function definition rather than expecting the student to guess what domain is expected.

But, assuming the questioner means "The domain is the set of real numbers less any values that are inadmissible", then the inadmissible values are x = -2 and x = +3, because at these x values the f(x) value cannot be computed as it would involve division by zero.

As x tends to + or - infinity the graph approaches f(x) = 3x^2 so there are no horizontal asymptotes.

g(x) : the quadratic can be similarly factorised to give the asymptotes and inadmissible values.

As x tends to + or - infinity the graph approaches g(x) = 2x. As this is a line, it counts as an asymptote, but it is not horizontal.

Bob

You cannot teach a man anything; you can only help him find it within himself..........Galileo Galilei

Offline

**skylor****Guest**

I'm sorry I must have written the problem wrong

it should be f(x) = 3x^2+4 over x^2 -x -6. If you understand what I mean

**bob bundy****Moderator**- Registered: 2010-06-20
- Posts: 6,269

Well no I don't. I thought you meant

and that's the question I tried to answer in post 5.

If that isn't right then the only other interpretation I can think of is

That has x = 0 as an asymptote and doesn't cross the y axis at all.

**This shows the importance of correct placing of brackets.**

Oh wait a minute. Did you mean:

In which case, same asymptotes as post 5 and same crossing .... in fact all the answers are unchanged, except .....

As x tends to infinity the function tends towards

So now we have a horizontal asymptote.

Bob

You cannot teach a man anything; you can only help him find it within himself..........Galileo Galilei

Offline

**Skylor****Guest**

Yes that it was I meant thanks!

Pages: **1**