Consider all quadratic equations with real coefficients:
y=ax2+bx+c,a,b,c∈R,a≠0
I was wondering whether if more of them have real roots, more have complex roots, or a same number of each?
I thought about this graphically, and wlog considered only the ones with positive a. By categorising the quadratics by their minimum point, there are an equal number of possible minima below the x-axis as above, so it seems that there are an equal number of quadratics with real roots as complex ones.
However, I then considered this problem algebraically by using the discriminant:
b2−4ac
If a and c have opposite signs, then the discriminant will be positive, and so the quadratic will have real roots. This represents 50% of the quadratic equations possible.
However, if a and c have the same sign, then some of these quadratics have real roots, whilst others have complex roots depending on whether 4ac is bigger than b2 or not.
This suggests that there are more quadratics with real roots which contradicts the above answer.
Is the reason I've reached contradicting answers something to do with infinites, and that I can't really compare them in the way I've done above?
No comments:
Post a Comment