My Math Forum  

Go Back   My Math Forum > High School Math Forum > Algebra

Algebra Pre-Algebra and Basic Algebra Math Forum

LinkBack Thread Tools Display Modes
September 5th, 2011, 03:26 PM   #1
Senior Member
Joined: Jun 2011

Posts: 154
Thanks: 0


Hello Everyone. Among plenty more problems in my precalculus class that I am having trouble with, this is one that has me the most baffled. If someone could please solve it and tell me how they did so I would be extremely grateful.

Here it is:

f(x) = 2x-5x ; g(x) = 2x/x-5 (two x over x minus 5)

All I am asked is to find fg

I have been trying to solve this for a good while, and honestly, I am not sure if it is asking me to multiply the two functions, or to find f(g). Either way, I tried doing both and got no answer that was anywhere near the 5 choices given by my instructor, which are listed below. (note, 2x^5 means 2x to the 5th power etc.. If someone knows the ASCII code for "superscripts 4 and 5", please share them with me).

1. 2x^5+25x-75x
2. 2x^5-25x-75x
3. 2x^5+16x^4+25x-40x-75x
4. 2x^5+16x^4-35x-40x-75x
5. 2x^5+16x^4+25x+40x+75x

These are the answer choices given to me, and neither me or my friend/classmate have been able to make much sense of this. If anyone out there can help, that would be awesome. Thanks, and have a great day!
jkh1919 is offline  
September 5th, 2011, 03:49 PM   #2
Global Moderator
Joined: May 2007

Posts: 6,641
Thanks: 625

Re: Precalculus

Something is screwed up. When you multiply you get 4x^3 - 2x^2. f(g) leads to a rational function with both numerator and denominator has cubic polynomials.
mathman is offline  
September 5th, 2011, 04:04 PM   #3
Senior Member
Joined: Jun 2011

Posts: 154
Thanks: 0

Re: Precalculus

Wow..thank you for pointing that out. I've literally been doing math homework for 2 days straight, I think it's time for a break. But regardless, here is the CORRECT problem. I was trying to figure it out last night and couldn't.

f(x) = 2x-5x
g(x) = x+8x+15

These are correct, I double checked twice, as well as the answer choices I gave in my original post.
jkh1919 is offline  
September 5th, 2011, 05:32 PM   #4
Global Moderator
greg1313's Avatar
Joined: Oct 2008
From: London, Ontario, Canada - The Forest City

Posts: 7,885
Thanks: 1088

Math Focus: Elementary mathematics and beyond
Re: Precalculus

It looks like f * g.

(2x - 5x)(x + 8x + 15) = 2x^5 + 16x^4 + 25x^3 - 40x^2 - 75x, choice number 3.
greg1313 is offline  

  My Math Forum > High School Math Forum > Algebra


Thread Tools
Display Modes

Similar Threads
Thread Thread Starter Forum Replies Last Post
WHAT is the math before precalculus? magichands Academic Guidance 5 February 22nd, 2013 01:49 AM
Precalculus daivinhtran Algebra 1 September 18th, 2011 09:55 AM
precalculus jjoiner Algebra 1 September 1st, 2011 07:25 AM
PreCalculus amanda_ Pre-Calculus 4 August 14th, 2010 06:21 PM
precalculus jjoiner New Users 0 December 31st, 1969 04:00 PM

Copyright © 2018 My Math Forum. All rights reserved.