(Arccos(-1/2)-arcsin1/2)^2-1
1)arccos(-1/2)=π-arccos1/2=π-π/3=2π/3
2)arcsin1/2=π/6
3) 2π/3-π/6=π/2
4)(π/2)²-1=π²/4-1=(π²-4)/4