It is known that the function f (x) is an even function defined on R. when x ≥ 0, f (x) = - x ^ 2 + 4x It is known that the function f (x) is an even function defined on R. when x ≥ 0, f (x) = - x ^ 2 + 4x. Solution: the equation f (x) = k has four different real roots, and the value range of K is obtained

It is known that the function f (x) is an even function defined on R. when x ≥ 0, f (x) = - x ^ 2 + 4x It is known that the function f (x) is an even function defined on R. when x ≥ 0, f (x) = - x ^ 2 + 4x. Solution: the equation f (x) = k has four different real roots, and the value range of K is obtained

Because even function f (- x) = f (x) = - x ^ 2-4x draws function image, it is easy to see 4 > k > 0