If tan−1 x+tan−1 y=4π5,then cot−1 x+cot−1 y equals to
(a) π5 (b) 2π5 (c) 3π5 (d) π
If sin−1x+sin−1y=π2,then cos−1x+cos−1y is equal to
If cos−1x+cos−1y=π2 and tan−1x−tan−1y=0 then x2+xy+y2 is equal to