Question

If a,b are the roots of equation x^2+3x+4=0 then a+b = ?

Answer 1

That equation has no real roots.

But actually has complex ones and they can be added
Symply by using the following formula:

If x1 and x2 are the roots of the ecuation
ax^2+bx+c =0

Then x1+x2 = -b/a

In this case that happens to be -3.