sis 2011 concavity/convexity doubt

[varnika1880]

The utility function (x^a  -1)/a
a{0,1} x{R+}
(a) concave and increasing
(b) convex and increasing
(el concave and decreasing ~
(d) convex and decreasing

[Dreyfus]

[varnika1880]

Thanks a lot ..