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NDA 2021
Exam
NDA
Year
2021
Subject
Mathematics
Chapter
Trigonometric Ratios & Identities
NDA 2021 · Mathematics · Trigonometric Ratios & Identities
What is (1+ θ-cosec θ)(1+ θ+ θ) equal to?
What is
(
1
+
cot
θ
−
cosec
θ
)
(
1
+
tan
θ
+
sec
θ
)
(1+\cot \theta-\operatorname{cosec} \theta)(1+\tan \theta+\sec \theta)
(
1
+
cot
θ
−
cosec
θ
)
(
1
+
tan
θ
+
sec
θ
)
equal to?
Options
A
1
1
1
B
2
2
2
C
3
3
3
D
4
4
4
Correct answer
B.
2
2
2
Step-by-step solution
(
1
+
cot
θ
−
cosec
θ
)
(
1
+
tan
θ
+
sec
θ
)
=
(
sin
θ
+
cos
θ
−
1
sin
θ
)
(
sin
θ
+
cos
θ
+
1
cos
θ
)
\begin{aligned} & (1+\cot \theta-\operatorname{cosec} \theta)(1+\tan \theta+\sec \theta) \\ & =\left(\frac{\sin \theta+\cos \theta-1}{\sin \theta}\right)\left(\frac{\sin \theta+\cos \theta+1}{\cos \theta}\right)\end{aligned}
(
1
+
cot
θ
−
cosec
θ
)
(
1
+
tan
θ
+
sec
θ
)
=
(
sin
θ
sin
θ
+
cos
θ
−
1
)
(
cos
θ
sin
θ
+
cos
θ
+
1
)
=
(
sin
θ
+
cos
θ
)
2
−
1
2
sin
θ
⋅
cos
θ
=
sin
2
θ
+
cos
2
θ
+
2
sin
θ
⋅
cos
θ
−
1
sin
θ
⋅
cos
θ
\begin{aligned} & =\frac{(\sin \theta+\cos \theta)^2-1^2}{\sin \theta \cdot \cos \theta} \\ & =\frac{\sin ^2 \theta+\cos ^2 \theta+2 \sin \theta \cdot \cos \theta-1}{\sin \theta \cdot \cos \theta}\end{aligned}
=
sin
θ
⋅
cos
θ
(
sin
θ
+
cos
θ
)
2
−
1
2
=
sin
θ
⋅
cos
θ
sin
2
θ
+
cos
2
θ
+
2
sin
θ
⋅
cos
θ
−
1
=\frac{1+2 \sin \theta \cdot \cos \theta-1}{\sin \theta \cdot \cos \theta}=2$
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