On the Ulam stability of a quadratic set-valued functional equation

In this paper, we prove the Ulam stability of the following setvalued functional equation by employing the direct method and the fixed point method, respectively, \[f ( x \frac{ y + z}{ 2}) \oplus f (x +\frac{ y z}{ 2})\oplus f(x + z) = 3f(x) \oplus \frac{1}{ 2} f(y) \oplus \frac{3 }{2 }f(z).\]