Let f: R → R be defined as f(x)= {-55 x, if x<-5; 2 x^3-3 x^2-120 x, if -5 ≤ x ≤ 4; 2 x^3-3 x^2-36 x-336, if x>4,} Let A ={x ∈ R: f is increasing }.…

Let $\displaystyle f: \mathbf{R} \rightarrow \mathbf{R}$ be defined as $$f(x)= \begin{cases}-55 x, & \text { if } x<-5 \\ 2 x^3-3 x^2-120 x, & \text { if }-5 \leq x \leq 4 \\ 2 x^3-3 x^2-36 x-336, & \text { if } x>4,\end{cases} $$ Let $\displaystyle \mathrm{A}=\{x \in \mathbf{R}: f$ is increasing $\displaystyle \}$. Then A is equal to :