8) arcCos(-1/2) - arcSin1/2 = 2π/3 - π/6 = 3π/6 = π/2
9) arcCos(-1/2) + arcSin(-1) = 2π/3 -π/2 = π/6
10)arcCos(-1/2) + arcSin√2/2 = 2π/3 + π/4 = 11π/12
11) arcCos(-1) + arcSin (-1/2) = π -π/6 = 5π/6
12)-arcCos(-1/2) + arcSin(-1/2) = -2π/3 - π/6 = -5π/6
13) arcCos(-√3/2) - arcSin1/2 = 5π/6 - π/6 = 4π/6 = 2π/3