Khai triển Maclaurin của cosx đến x4

\[1 - \frac{{{{\rm{x}}^2}}}{2} + \frac{{{{\rm{x}}^4}}}{{24}} + {\rm{o}}({{\rm{x}}^5})\]

\[1 + \frac{{{{\rm{x}}^2}}}{2} - \frac{{{{\rm{x}}^4}}}{{24}} + {\rm{o}}({{\rm{x}}^5})\]

\[1 - \frac{{{{\rm{x}}^2}}}{2} - \frac{{{{\rm{x}}^4}}}{{24}} + {\rm{o}}({{\rm{x}}^5})\]

\[1 + \frac{{{{\rm{x}}^2}}}{2} + \frac{{{{\rm{x}}^4}}}{{24}} + {\rm{o}}({{\rm{x}}^5})\]