Tan−1pq+Tan−1q−pq+p=
π4
π2
3π4
−π4
We have, tan-1pq+tan-1q-pq+p=tan-1pq+tan-11-pq1+pq since tan-1x-y1+xy=tan-1x-tan-1y =tan-1pq+tan-11-tan-1pq =π4