Let f(x) = -x³ + 2x² + 2. Find an open interval (a,b) on which f increases. Provide a and b in decimal form with three significant digits after the decimal point.
a) (0.731, 1.465)
b) (0.500, 1.732)
c) (0.866, 1.155)
d) (0.231, 1.923)