Laboratory Project in Sec.3.10, Calculus by Stewart Chinese version: 泰勒級數 The tangent line approximation $L(x)$ is the best first-degree (linear) approximation to $f(x)$ near $x=a$ because $f(x)$ and $L(x)$ have the same rate of change (derivative) at $x=a$. For a better approximation than a linear one, let’s try a second-degree (quadratic) approximation $P(x)$. In other words, we approximate a curve by a parabola instead of a straight