Answer
a) False b) False c) True
Work Step by Step
a) $\dfrac{d}{dx}[\dfrac{(2x+1)^3}{3} +C]=\dfrac{1}{3}(3 (2x+1)^2)(2)\ne (2x+1)^2$; False
b) $\dfrac{d}{dx}[(2x+1)^3 +C]=(3 (2x+1)^2)(2)\ne
3(2x+1)^2$; False
b) Since,we have $\dfrac{d}{dx}[(2x+1)^3 +C]=(3 (2x+1)^2)(2) =6(2x+1)^2$; True