Use the Lagrange remainder to determine how many terms of the Taylor series of cos expanded at 0 are needed to estimate $cos(\frac{21\pi}{5})$ . Accuracy to 3 decimal places
So I have a lot of rough work on paper. I know math.stackexchange dosn't really answer assignment questions but I am looking for a head start on even where to start.
If you guys want, i can type up my notes here. Bascically the f'(c) term from the lagrange formula can be 1. I know my inequality has something to do with < 0.001. I need taylor's expansion (obviously to find the n I need).
I just can't put it together. This is my first real-analysis course.