This is a problem from Apostol's Calculus (p. 209 Ex. 26 (c) & (d)). The problem is to find a function $f$ with a continuous second derivative $f''$ satisfying the following conditions:
(c) $f''(x) > 0 \quad \text{for every } x, \qquad f'(0) = 1, \qquad f(x) \leq 100 \quad \text{for all } x > 0$.
(d) $f''(x) > 0 \quad \text{for every } x, \qquad f'(0) = 1, \qquad f(x) \leq 100 \quad \text{for all } x < 0$.
So, for part (c) I do not think such a function can exist. My proof is that $f''(x) > 0$ for every $x \implies f'(x)$ is increasing. Since $f'(0) = 1$ this means $f'(x) > 1$ for $x > 0$.
By the mean value theorem we have $f(b) - f(0) = f'(c) (b)$ for some $c \in (0,b)$. Since $f'(c) > 1$ for all $c \in (0,b)$ we have $f(b) > b + f(0)$ for any $b > 0$. So, just choose $b > 100 + |f(0)|$ to obtain $f(b) > 100$ contradicting that $f(x) \leq 100$ for all $x > 0$.
Is this a sensible approach? I feel like there should be a more straightforward way to get to this.
For (d) it seems to me that there should be some function to satisfy these restrictions (since for $x < 0$ we can certainly let $f$ take on arbitrarily large negative values). It isn't clear to me how to systematically identify such a function though.
This problem comes from the exercises immediately following the statement and proofs of the first and second fundamental theorems of calculus, and a brief section on deducing properties of a function from its derivative; such as, a nonnegative derivative on an interval $\implies$ the function is increasing on the interval.