Question

Prove that Tan inverse 1/7+ tan inverse 1\8=tan inverse 3\11

Answer 1

we know that arc tan A+arc tan B=

arc tan (a+b/1-ab)

so, arc tan1/7+arc tan1/8=

arc tan (1/7+1/8/1-1/7×1/8)

arc tan(7+8/7×8/1-1/56)

arc tan(15/56/55/56)

arc tan(15/55)

arc tan(3/11).