Consider two functions $f: \mathbb{R} \rightarrow \mathbb{R}$ and $g: \mathbb{R} \rightarrow(1, \infty)$. Both functions are differentiable at a point c . Which of the following functions is/are ALWAYS differentiable at c ? The symbol $\cdot$ denotes product and the symbol odenotes composition of functions.

$$\mathop {\lim }\limits_{t \to + \infty } \sqrt{t^2+t}-t= $$

(Round

off to one decimal place)