It just has to be tangent. So that line has to be tangent to our function right at that point. So our function f could look something like that. So when they say find f prime of two, they're really saying what is the slope of the tangent line when x is equal to two? So when x is equal to two, well, the slope of the tangent line is the slope of this line. They gave us, they gave us the two points that sit on the tangent line. So we just have to figure out its slope, because that is going to be the rate of change of that function right over there.