Concept:An even function satisfies symmetry about the y-axis.Explanation:The definition of an even function is f(−x)=f(x) for all x in the domain.This means the function's value at −x equals its value at x.Option A: −f(x)=f(x) implies f(x)=0, which is a specific case, not the general definition.Option C: f(−x)=−f(x) defines an odd function.Thus, the correct condition for an even function is f(−x)=f(x).Answer:f(−x)=f(x)