Answer:
A, C
Explanation:
Quadratic formula:

a is the coefficient of x², b is the coefficient of x and c is the constant when a second degree polynomial is equal to zero. (ax² +bx +c= 0)
x² +5x +11= 0
a= 1, b= 5, c=11
Thus, using the quadratic formula:

∴The answers are A and C.