A-LEVEL MATHEMATICS Topic : Using Discriminants to Find the Number of Roots of a Quadratic Curve

In general a quadratic curve may have one, two or no roots, as shown.

For the curve the number of roots depends entirely on the discriminant
Ifthere are no roots.
Ifthere is one root.
Ifthere are two roots.
We are typically asked: Find the set of values offor which the curve has
no roots:
always, for every value ofso for every value of k the curve has two roots.
Example: Find the set of values offor which the curvehas two roots.
We solve for
So solutions exist for all values of
Example: Find the set of values offor which the curvehas one root.
We solve for

Soor