[1/tan(a/2)-tan(a/2)]×](1+tan a×tan(a/2)]={[cos²(a/2)-sin²(a/2)]/[cos(a/2)×sina/2]}×{[cosa×cos(a/2)+sina×sin(a/2)]/[cosa×cos(a/2)]}={2[1/2+cosa/2-1/2+cosa]/[2cos(a/2)×sina/2]}×{cos(...