lim(x-->0) (cosx - 1)/x²= lim(x-->0) [1 - 2sin²(x/2) - 1]/x²= lim(x-->0) - 2sin²(x/2)/(x/2)² * 1/4= lim(x-->0) [sin(x/2)/(x/2)]² * -1/2= -1/2