cos−1p+cos−1q+cos−1r=3π We know that, if y=cos−1x, then −1≤x≤1 and 0≤y≤π. Hence, the given equation will hold only when each is π. ∴p=q=r=cos‌π=−1 ∴p2+q2+r2+2pqr =(−1)2+(−1)2+(−1)2+2(−1)(−1)(−1) =1+1+1−2=3−2=1