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Byju's Answer
Standard X
Mathematics
Trigonometric Identities
in trigonomet...
Question
in trigonometry, when do we substitute a formula, use LCM, multiply it with something ??
eg:
root of 1+cosA/1-cosA + root of 1-cosA/1+cosA
sin^4A-cos^$A=1-2cos^2A
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Solution
1
+
cos
A
1
-
cos
A
+
1
-
cos
A
1
+
cos
A
=
1
+
cos
A
+
1
-
cos
A
1
-
cos
A
1
-
cos
A
=
2
1
-
cos
2
A
as
,
1
-
cos
2
A
=
sin
2
A
=
2
sin
A
=
2
cosec
A
as
,
1
sin
A
=
cosec
A
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Similar questions
Q.
Prove the identity:
s
i
n
A
+
c
o
s
A
s
i
n
A
−
c
o
s
A
+
s
i
n
A
−
c
o
s
A
s
i
n
A
+
c
o
s
A
=
2
1
−
2
c
o
s
2
A
Q.
Prove that :
s
i
n
A
+
c
o
s
A
s
i
n
A
−
c
o
s
A
+
s
i
n
A
−
c
o
s
A
s
i
n
A
+
c
o
s
A
=
2
s
i
n
2
A
−
c
o
s
2
A
=
2
2
s
i
n
2
A
−
1
=
2
1
−
2
c
o
s
2
A
Q.
Out of the following four relations:
(I)
s
i
n
A
1
+
c
o
s
A
+
s
i
n
A
1
−
c
o
s
A
=
2
s
i
n
A
(II)
(
1
+
c
o
s
A
s
i
n
A
)
2
=
1
+
c
o
s
A
1
−
c
o
s
A
(III)
s
i
n
10
o
c
o
s
80
o
= 1
(Iv)
s
i
n
4
A
−
c
o
s
4
A
=
1
+
s
i
n
2
A
the wrong one is
Q.
Prove that
√
1
−
c
o
s
A
1
+
c
o
s
A
+
√
1
+
c
o
s
A
1
−
c
o
s
A
=
2
c
o
s
e
c
A
Q.
The expression
E
=
c
o
t
A
−
c
o
s
A
c
o
t
A
+
c
o
s
A
is the same in value in which of the following expressions?
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