A linear approximation to a function at a point can be computed by taking the first term in the Taylor series
Linear Approximation
See also
Maclaurin Series, Taylor SeriesExplore with Wolfram|Alpha
Cite this as:
Weisstein, Eric W. "Linear Approximation." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/LinearApproximation.html