Here is your first calculus lesson: try to find the line tangent to the graph of y = x^2, at x=1.
this means finding the graph of the linear function closest to x^2, near x=1.
well consider how x^2 changes as x changes near 1. we have x = 1+h so x^2 =
(1+h)^2 = 1+ 2h + h^2, where h = x-1.
Now the linear part of this expression is 2h, and for x near 1, i.e. small h, h^2 is extremely small. e.g. h=.1 implies h^2 = .01.
So the linear approximation to x^2 near x=1 seems to be 1^2 +2h, or 1+2(x-1).
Thus near x=1, the linear function closest to x^2 seems to be y = 2x-1.
This says the tangent line to y=x^2, at x= 1, should be the graph of y = 2x-1.
more generally, this method shows the linear approximation to y = x^2 near x = a,
is y = a^2 + 2a(x-a).