Question

solve it by taking (2a +1)and( a-1) common
solve it in a page so that it could be easy to understand
solution must be step by step
irrelevant answers will be reported^_^

Answer 1

is it correct?
if not u van report

Answer 2

Proof:
Let x=2a+1 andy=a-1

We know the well-known formula

(x-y)³=x³- 3 x²y+ 3 xy² - y³

By transposition,

x³ - y³ = (x-y)³ + 3 x²y - 3 xy²

x³ - y³ = (x-y)³ +3 xy(x-y)

x³ - y³ = (x-b) [(x-y)² +3 xy]

x³ - y³ = (x-b) [(x-y)² +3 xy]

We all know (x - y)² = x² - 2 xy + b²

So

x³ - y³ = (x-y) [(x² - 2 xy + y²) +3 xy]

x³-b³= (x-y)(x²+xy+ y²) [Proved]
put the values of x and y to get the final answer.
Hope it helps.