cos−1(1/3)\cos ^{-1}(1 / \sqrt{3})cos−1(1/3)
cos−1(1/3)\cos ^{-1}(1 / 3)cos−1(1/3)
cos−1(1/2)\cos ^{-1}(1 / 2)cos−1(1/2)
cos−1(1/2)\cos ^{-1}(1 / \sqrt{2})cos−1(1/2)