We know that cube of a negative number is negative
(-m)3 = -m3
thus, the given expression can be written as a3 + (-b)3 + (-c)3 - 2abc
a3 + b3 + c3 - 3abc = (a+b+c) (a2+b2+c2-ab-bc-ca)
But, if a+b+c = 0, then
a3+b3+c3 - 3abc = 0
In this case, a = a – 4.36; b = -b = =2.39 and c = -c = 1.97
a+b+c = 4.36 + (-2.39) + (-1.97) = 0
a3+b3+c3 - 3abc = 0