NCERT Class XI Mathematics - Trigonometric Functions - Solutions

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Question : 45
Total: 61
cot x = − 3
Solution:  
cot x = − 3 ⇒ tan x =
1
3

A value of x satisfying tanx =
1
3
is
π
6

Principal Solution : We have tanx =
1
3

Thus , tan (π
π
6
)
= - tan
π
6
=
1
3
and , tan (2π
π
6
)
= - tan
π
6
= -
1
3

Thus , tan
5π
6
= tan
11π
6
=
1
3

Therefore principal solutions are
5π
6
,
11π
6

General Solution :
We have, tanx =
1
3

⇒ tan x = tan (π
π
6
)
= tan
5π
6
⇒ x = nπ +
5π
6
, n ∊ Z
Since tan x = tan α , then x = nπ + α , n ∊ Z
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