It is known that f (x) is an even function and an increasing function on (0, + ∞) It is known that f (x) is an even function and is an increasing function on (0, + ∞). It is proved that f (x) is an increasing function or a decreasing function on (- ∞, 0)

It is known that f (x) is an even function and an increasing function on (0, + ∞) It is known that f (x) is an even function and is an increasing function on (0, + ∞). It is proved that f (x) is an increasing function or a decreasing function on (- ∞, 0)

prove:
Take 0