Why when the discriminant equals zero the equation is a quadratic

One card is dealt from a 52 card deck. find the probability that the dealt card is a 4 or a black 7

Aschool puts on a play. the play costs $1,200 in expenses. the students charge $4.00 for tickets. there will be one performance of the play in an auditorium that seats 500 people. what is the domain of the function that shows the profit as a function of the number of tickets sold?  

It says factor each expression completely 8y+48