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Trigonometric Ratios & Identities
NDA 2017
Exam
NDA
Year
2017
Subject
Mathematics
Chapter
Trigonometric Ratios & Identities
NDA 2017 · Mathematics · Trigonometric Ratios & Identities
If θ=3 (θ+2 α) , then the value of (θ+α)+2 α is equal to
If
sin
θ
=
3
sin
(
θ
+
2
α
)
\sin \theta=3 \sin (\theta+2 \alpha)
sin
θ
=
3
sin
(
θ
+
2
α
)
, then the value of
tan
(
θ
+
α
)
+
2
tan
α
\tan (\theta+\alpha)+2 \tan \alpha
tan
(
θ
+
α
)
+
2
tan
α
is equal to
Options
A
-1
B
0
C
1
D
2
Correct answer
B. 0
Step-by-step solution
Given,
sin
θ
=
3
sin
(
θ
+
2
α
)
⇒
sin
(
θ
+
2
α
)
sin
θ
=
1
3
\sin \theta=3 \sin (\theta+2 \alpha)\Rightarrow \frac{\sin (\theta+2 \alpha)}{\sin \theta}=\frac{1}{3}
sin
θ
=
3
sin
(
θ
+
2
α
)
⇒
s
i
n
θ
s
i
n
(
θ
+
2
α
)
=
3
1
Apply componendo and dividendo rule
⇒
sin
(
θ
+
2
α
)
+
sin
θ
sin
(
θ
+
2
α
)
−
sin
θ
=
1
+
3
1
−
3
⇒
2
sin
(
θ
+
α
)
cos
α
2
cos
(
θ
+
α
)
sin
α
=
4
−
2
=
−
2
⇒
tan
(
θ
+
α
)
tan
α
=
−
2
⇒
tan
(
θ
+
α
)
=
−
2
tan
α
⇒
tan
(
θ
+
α
)
+
2
tan
α
=
0
\begin{aligned} & \Rightarrow \frac{\sin (\theta+2 \alpha)+\sin \theta}{\sin (\theta+2 \alpha)-\sin \theta}=\frac{1+3}{1-3} \\ & \Rightarrow \frac{2 \sin (\theta+\alpha) \cos \alpha}{2 \cos (\theta+\alpha) \sin \alpha}=\frac{4}{-2}=-2 \\ & \Rightarrow \frac{\tan (\theta+\alpha)}{\tan \alpha}=-2 \\ & \Rightarrow \tan (\theta+\alpha)=-2 \tan \alpha \Rightarrow \tan (\theta+\alpha)+2 \tan \alpha=0 \end{aligned}
⇒
sin
(
θ
+
2
α
)
−
sin
θ
sin
(
θ
+
2
α
)
+
sin
θ
=
1
−
3
1
+
3
⇒
2
cos
(
θ
+
α
)
sin
α
2
sin
(
θ
+
α
)
cos
α
=
−
2
4
=
−
2
⇒
tan
α
tan
(
θ
+
α
)
=
−
2
⇒
tan
(
θ
+
α
)
=
−
2
tan
α
⇒
tan
(
θ
+
α
)
+
2
tan
α
=
0
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