Question

The value of a cube + b cube + c cube - 3abc if a+b+c=15 and ab+bc+ca=74 is

Answer 1

Take help of pic.. M

Answer 2

Hi,Remember this formula and you are one step ahead in expansions:

a^3+b^3+c^3-3abc=(a+b+c)(a^2+b^2+c^2-ab-bc-ca).......(1)

(a+b+c)^2=a^2+b^2+c^2+2(ab+bc+ca)

=15^2=a^2+b^2+c^2+2*74=a^2+b^2+c^2=225-148

=a^2+b^2+c^2=77

Put this value in (1) and you are done!

a^3+b^3+c^3-3abc

=15(77-74)

=15*3=45

Sweet, thats the answer