How do you use quadratic formula on ti 89?

The function on a ti-89 that gives you the zeros of a quadratic equation is called just that "zeros". To access it from the home screen, press f2 and select the label called "zeros(" then type the function and define the variable. For example:

if you want the zeros of y=x^2+7x+12 you the display should read:

zeros(x^2+7x+12,x), press enter and it will give you the results in this case {-3, -4}.

We can check if it did it right by factoring this simple quadratic. 0=x^2+7x+12 factors as 0=(x+3)(x+4) set the factors equal to zero:

x+3=0 x=-3

x+4=0 x=-4

So we see that the calculator did it right! That is always a good thing. This will work for most polynomial functions.