The result tan–1 x – tan–1(x - y/1 + xy) is true when value of xy is > -1.
We have,
Applying, tan-1 both sides, we get,
So, from (3),
tan-1tan(A-B) = A-B
So, from (3),
tan-1tan(A-B) = A-B
⇒ tan A tan B < -1
As, tan B < 0
xy > -1
Now, if A < 0 and B > 0,
Applying tan on both sides,