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
May 5th, 2018, 09:07 AM   #1
Joined: May 2018
From: Bucharest

Posts: 1
Thanks: 0

Need some help with this..I don't know what to do at b)

Christiane3 is offline  
May 5th, 2018, 09:22 AM   #2
Senior Member
romsek's Avatar
Joined: Sep 2015
From: USA

Posts: 2,264
Thanks: 1198

at worst you can just evaluate the determinant.

$d = a(a^2-bc) - b(ac -b^2) + c(c^2-ab)$

then a bit of algebra will get you to the result they want. I leave that to you.
romsek is offline  
May 5th, 2018, 09:32 AM   #3
Global Moderator
Joined: Dec 2006

Posts: 20,098
Thanks: 1905

If you've done part (a), you know how to evaluate a 3×3 determinant.

Hence you should understand why d = a³ + b³ + c³ - 3abc.

The right-hand side factorizes as (a + b + c)(a² + b² + c² - ab - ac - bc),
which can easily be shown to be equivalent to the expression for d given in part (b).
skipjack is offline  

  My Math Forum > High School Math Forum > Algebra


Thread Tools
Display Modes

Copyright © 2019 My Math Forum. All rights reserved.