Answer:
[tex]{ \tt{pq( {r}^{2} + 1) - r( {p}^{2} + {q}^{2} ) }} \\ \\ \dashrightarrow \: { \tt{pq \{ {(r + 1)}^{2} - 2r \} - r \{ {(p + q)}^{2} - 2pq \} }} \\ \\ \dashrightarrow \:{ \tt{pq {(r + 1)}^{2} - 2pqr - r {(p + q)}^{2} + 2pqr}} \\ \\ \dashrightarrow \: { \tt{pq {(r + 1)}^{2} - r {(p + q)}^{2} }}[/tex]
