Question

a=3+b , then a^{​​​​​​3} - b^{​​​​​​3}​​​​​-9ab is

Answer 1

a^3-b^3-9ab
subs value of a
=(3+b)^3-b^3 -9(3+b)×b
=(3)^ 3 +b^3+3×3×b (3+b) =27+b^3+9b (3+b)-b^3-9b (3+b)
=27+27b+9b^2-27b-9b^2 =27