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Byju's Answer
Standard X
Mathematics
Trigonometric Ratios of a Right Triangle
If sinθ is ...
Question
If
sin
θ
is G.M of
sin
ϕ
and
cos
ϕ
, then prove that
cos
2
θ
=
2
cos
2
(
π
4
+
ϕ
)
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Solution
sin
2
θ
=
sin
ϕ
cos
ϕ
2
sin
2
θ
=
sin
2
ϕ
1
−
cos
2
θ
=
−
cos
(
π
/
2
+
2
ϕ
)
∴
cos
2
θ
=
1
+
cos
(
π
/
2
+
2
ϕ
)
cos
2
θ
=
2
cos
2
(
π
4
+
ϕ
)
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Q.
If
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Q.
Show that
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If
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