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\frac{d}{d x} \sin (a x+b)=\cos (a x+b) D(a x+b)=a \cdot \cos (a x+b) \quad \frac{d}{d t}\left(e^{3 t}\right)=e^{3 t} \frac{d}{d t}(3 t)=3 \cdot e^{3 t}