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Byju's Answer
Standard XI
Mathematics
Trigonometric Ratios of Half Angles
If cos A2=b+c...
Question
If
cos
A
2
=
√
b
+
c
2
c
, then :
A
a
2
+
b
2
=
c
2
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B
c
2
+
b
2
=
a
2
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C
a
2
+
c
2
=
b
2
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Solution
The correct option is
A
a
2
+
b
2
=
c
2
cos
A
2
=
√
b
+
c
2
c
⇒
s
(
s
−
a
)
b
c
=
b
+
c
2
c
⇒
2
s
(
2
s
−
2
a
)
=
2
b
(
b
+
c
)
⇒
(
b
+
c
+
a
)
(
b
+
c
−
a
)
=
2
b
2
+
2
b
c
⇒
(
b
+
c
)
2
−
a
2
=
2
b
2
+
2
b
c
⇒
c
2
=
a
2
+
b
2
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Q.
If
cos
A
2
=
√
b
+
c
2
c
, then :