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\mathbf{D}(2 \sqrt{5 x+3})=2 \cdot \frac{1}{2}(5 x+3)^{-1 / 2} \mathbf{D}(5 x+3)=5 \cdot(5 x+3)^{-1 / 2}=\frac{5}{\sqrt{5 x+3}}