I expect you are trying to factor this. You can use the method of decomposition, as follows:
In ax^2 + bx + c, find the product of a and c. Then find two numbers that multiply to ac and add to b...
For 5x^2 + 6x + 11, ac = 55 and b = 6. The factor pairs for 55 are 1, 55; 5, 11. Since neither of these pairs add to 6, the expression is PRIME, or not factorable over the integers. Are you sure you did not flip a sign somewhere (i.e., it would be factorable if either a or c were negative)?
If you are trying to evaluate the expression at a given value of x, you would need to specify that value.