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concave :
wklęsłykɑnˈkeɪv
If f(x) is twice-differentiable, then f(x) is concave if and only if f ′′(x) is non-positive. Jeżeli f(x) jest dwukrotnie różniczkowalne, to f(x) jest wklęsłe wtedy i tylko wtedy, gdy f ′′(x) jest niedodatnie.
Any linear function is both concave and convex. Każda funkcja liniowa jest zarówno wklęsła jak i wypukła.
It is concave on the interval (-∞,0). Jest wklęsła w przedziale (-∞, 0).