TeX source:

\mathbf{D}\left((3 x+8)^{1 / 2}\right)=\frac{1}{2} \cdot(3 x+8)^{-1 / 2} \mathbf{D}(3 x+8)=\frac{3}{2} \cdot(3 x+8)^{-1 / 2}