Let u = {2,4,1-a}, a = {2,a2-a + 2}, if CUA = {- 1}, find the value of real number a

Let u = {2,4,1-a}, a = {2,a2-a + 2}, if CUA = {- 1}, find the value of real number a


Because CUA = {- 1}, so - 1 = 1-A, when a = 2A = 2, a2-a + 2 = 4 satisfies CUA = {- 1}