In later courses, you will learn that the cosine function can be written as
the sum of an infinite sequence. In particular, for \(x\) in radians, the cosine
function can be approximated by the finite series:
$$
\cos x \approx 1-\frac{x^{2}}{2 !}+\frac{x^{4}}{4 !}
$$
a. Graph \(Y_{1}=\cos x\) and \(Y_{2}=1-\frac{x^{2}}{2 !}+\frac{x^{2}}{4 !}\) on
the graphing calculator. For what values of \(x\) does \(Y_{2}\) seem to be a good
approximation for \(Y_{1} ?\)
b. The next term of the cosine approximation is \(-\frac{x^{6}}{6 !}\) Repeat
part a using \(Y_{1}\) and
\(Y_{3}=1-\frac{x^{2}}{2 !}+\frac{x^{4}}{4 !}-\frac{x^{6}}{6 !}\) For what
values of \(x\) does \(Y_{3}\) seem to be a good approximation for \(Y_{1} ?\)
c. Use \(Y_{2}\) and \(Y_{3}\) to find approximations to the cosine function
values below. Which
function gives a better approximation? Is this what you expected? Explain.
\(\begin{array}{llll}{\text { (1) } \cos -\frac{\pi}{6}} & {\text { (2) } \cos
-\frac{\pi}{4}} & {\text { (3) } \cos -\pi}\end{array}\)