ok so you used a different calc i guess.
The best online calc for this sort of thing is "Desmos Graphing calculator"
Have you used that one?
Oh, I repeat, have you learned the quadratic formula yet ?
https://www.youtube.com/watch?v=O8ezDEk3qCg
In this question
2x2+5x+3=0
a=2 b=5 and c=3
if you sub these values into the quadratic formula (which you will eventually have to memorize)
you will get x=-1 and x=-1.5 [You won't have to graph it.]