Find the values of 'a' for which the function f(x) = b - ax + sin x is increasing on mathbbR…

$f'(x) = -a + \cos x \ge 0$ for all $x \in \mathbb{R}$, so $a \le \cos x$ for all $x$. Since the least value of $\cos x$ is $-1$, $a \le -1$. Ans: $a \in (-\infty, -1]$