3

3. [Maximum mark: 6]

The derivative of a function $f$ is given by $f'(x) = 4 + 2x - 3e^x$, where $x \in \mathbb{R}$.

(a) Find the values of $x$ for which $f$ is decreasing. [3]

(b) Find the values of $x$ for which the graph of $f$ is concave‑up. [3]