The Largest possible value of cos(x) is 1 so the smallest possible value of 1- cos x is 0. The smallest possible value of cos(x) is -1 so the largest possible value of 1- cos x is 2: [tex]0\le 1- cos x\le 2[/itex]. That means (dividing through be that because both 0 and go to 0, and is "sandwiched between them", it must also go to 0.