δ=(B+2)？ -4(B+ 1)=B？ ≥0

(1) When B=0 and δ = 0, the equation has two equal real roots-1, and only one element is counted in the set.

At this time, A={- 1}, so the sum of all elements in a is-1.

(2) when B≠0, δ >; Equation 0 has two unequal real roots, and set A has two elements.

Vieta theorem knows that the sum of two roots is -(B+2), that is, the sum of all elements in A is -(B+2).