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

 Algebra Pre-Algebra and Basic Algebra Math Forum

 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. $d = a(a^2-bc) - b(ac -b^2) + c(c^2-ab)$ then a bit of algebra will get you to the result they want. I leave that to you.
 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 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).

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