x趨近於0時,(1-cosx/2)是x的高階無窮小怎麼算?

x趨近於0時,(1-cosx/2)是x的高階無窮小怎麼算?

(1-cosx)/2 =(1-(1-2sin^2(x/2)))/2
=sin^2(x/2)
~=(x/2)^2
x趨近於0時,(1-cosx/2)是x的高階無窮小