Question 970773
With these three points and quadratic regression,

a=-2
b=-4
c=9

-2x^2-4x+9 = y(x)
(-1,10.8) is approximate

vertex is at x=-1,11  by the formula

{{{graph(300,300,-10,10,-10,20,-2x^2-4x+9)}}}

Calculator:
Go to STAT and choose 1 Edit.  Put the x values in L1, hitting enter after each one, then put the y values in L2, doing the same.  Then second MODE, to get out.

Got to STAT  CALC  and hit 5, for quadratic regression.  Then do 2nd 1 COMMA 2nd 2, COMMA then VARS Y-VARS and hit 1.  That will give you the a, b, and c.

To graph, go to 2nd Y= for STAT PLOT and for Plot 1 hit enter
Scroll down to scatter plot and hit enter
Then scroll down to x-list and hit L1
For y-list hit L2
For Mark hit enter
Then graph, using the appropriate window.