In ∆ABC, A is obtuse then
tanBtanC=1
tanBtanC<1
tanBtanC>1
tanBtanC=−1
A is obtuse . ⇒B+C<90°⇒B<90°-C⇒tan B<tan90°-C=cot C.=1tan C
⇒tanBtanC<1