Question

equivalent C++ expressions for the algebraic expressions - a + (b*b - 4ac) / 2a

Answer 1

suppose x=-a+(b*b-4ac)/2a
then, in c++ x can be written as

x= a*(-1)+((b*b-(4*a*c)))/(2*a)

Answer 2

should point out that if you wanted the quadratic formula, it should be
x=(-b+pow((b*b-4*a*c), 0.5))/(2*a)
you would have to import the cmath library to use pow