Question 585004
The quantity {{{b^2-4ac}}} is the determinant. This determines whether your solutions are real or complex. If {{{b^2-4ac}}} is positive, then you'll have two real solutions. In the first problem (#6), you found that {{{b^2-4ac=64}}}. Since this is a positive number, this means that you have two real solutions.



On the other hand, for problem #9, you got -100. This means that there are 2 complex solutions.


Hope this clears things up a bit. If not, let me know.