
Algebra PreAlgebra and Basic Algebra Math Forum 
 LinkBack  Thread Tools  Display Modes 
May 5th, 2018, 08:07 AM  #1 
Newbie Joined: May 2018 From: Bucharest Posts: 1 Thanks: 0  Need some help with this..I don't know what to do at b) 
May 5th, 2018, 08:22 AM  #2 
Senior Member Joined: Sep 2015 From: USA Posts: 2,122 Thanks: 1102 
at worst you can just evaluate the determinant. $d = a(a^2bc)  b(ac b^2) + c(c^2ab)$ then a bit of algebra will get you to the result they want. I leave that to you. 
May 5th, 2018, 08:32 AM  #3 
Global Moderator Joined: Dec 2006 Posts: 19,712 Thanks: 1806 
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 righthand 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). 