Algebra
posted by Mary .
I need a function rule for the following:
X Y
2 2
0 1
1 2

Well, it's not a straight line, since the change is y is not proportional the change in x. You could fit a very large number of functions to those threee points, but the simplest would be a parabola of the form
y = ax^2 + bx + c
You can use your three data points to solve for a, b and c.
2 = 4a  2b + c
1 = c
2 = a + 4b + c
This tells you right away what c is, so now you can solve for a and b 
I just need a function rule for the graph. ex. y=2x+1

I know what you are asking for. A function of the form y = mx + b won't fit all three points. That is why I chose a quadratic fucntion. Try completing what I started