Recall chain rule:
u = 2x +1; du = 2dx → dx = du2\frac{du}{2}2du
= 1⋅u42⋅4\frac{1 \cdot u^{4}}{2 \cdot 4}2⋅41⋅u4
= u48\frac{u^{4}}{8}8u4 → (2x+1)48\frac{(2x+1)^{4}}{8}8(2x+1)4 + C
