What is the value a^3 - b^3?

Question

(1) a^2 + ab + b^2 = 0

(2) a - b = 3b

rohit8865 · Answer

(1) a^2 + ab + b^2 = 0
or (a+b)^2-ab=0
(a+b)^2=ab
thus ab is >=0
Now as sum of all +ve number a^2 + ab + b^2 =0 then a &b are 0
thus a^3 - b^3=0.........suff

(2)a=4b
a & b could be any number ....not suff..

Ans A

yezz · Answer

a^3-b^3 = (a-b)(a^2 + ab + b^2 )

from 1

suff
from 2
a = 4b

(3b) (16b^2+4b^2+b^2)... no idea about b ... insuff

A

mvictor · Answer

let's start with 2

a-b = 3b
a=4b
a^3 = 64b^3
a^3 - b^3 = 63b^3 - not sufficient.

1. a^2 + b^2 = -ab - but it's impossible. a^2 and b^2 separately must be positive. only way to be so is that a^2 + b^2 = 0, and only way possible if a=0 and b=0.
sufficient.

What is the value a^3 - b^3?

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