In: Math
The principal value of tan-1(tan 3π/5) is _____________.
(a) 2π/5
(b) -2π/5
(c) 3π/5
(d) -3π/5
Answer : (b) -2π/5
Explanation :
We have to find the principal valve of tan-1 (tan 3π/5).
This can be written as:
tan-1 (tan 3π/5) = tan-1 (tan[π – 2π/5])
= tan-1 (- tan 2π/5)
[ since tan(π – x) = -tan x ]
= –tan-1 (tan 2π/5)
= –2π/5
Therefore,
Principal value of tan-1(tan 3π/5) is -2π/5.
(b) –2π/5