Example 3. $y=2^{x} \cdot \cos x$.
Solution. We have the derivative of the product (rule 3)) of functions contained in formulas 4) and 9): $y^{\prime}=\left(2^{x}\right)^{\prime} \cos x+2^{x}(\cos x)^{\prime}=$ $=2^{x} \ln 2 \cos x-2^{x} \sin x$