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A "decreasing function" is one that gets smaller as its input gets larger. For example, f(x) = -x, f(x) = 1/x {x > 0}.
What can functions like sqrt(x), ln(x) be called? They are always increasing, but the rate at which they are increasing always slows down. Their first-order derivatives are decreasing functions.
ln(x) is a ____ function
Such a function is called a concave function. This is because it is concave downwards (convex side upwards). A concave function may decrease (although your examples do not) if the gradient/derivative decreases past zero.
