For a differentiable function f, the sign of its derivative is recorded as follows:
(−∞,−2):+, \; x=−2:0, \; (−2,1):−, \; x=1:0, \; (1,∞):+.
a) State the interval(s) on which f is strictly increasing.
b) State the interval(s) on which f is strictly decreasing.