If a+b+c=6,a2+b2+c2=14 and abc=6, then a3+b3+c3 equals:
Competition practiceAlgebra
A18
B36
C54
D42
Step-by-Step Solution
First ab+bc+ca=[(a+b+c)2−(a2+b2+c2)]/2=(36−14)/2=11. Then a3+b3+c3=3abc+(a+b+c)(a2+b2+c2−ab−bc−ca)=18+6(14−11)=18+18=36. (The numbers are 1, 2, 3, and 1 + 8 + 27 = 36.)
Answer: B) 36
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