Prove that Cos^4 A- sin^4 A=cos 2A
Answers
Answered by
3
Answer:
Explanation:
We use the following identities
a
2
n
−
b
2
n
=
(
a
n
+
b
n
)
(
a
n
−
b
n
)
sin
2
x
+
cos
2
x
=
1
cos
(
a
+
b
)
=
cos
a
cos
b
−
sin
a
sin
b
Proof
cos
4
x
−
sin
4
x
=
(
cos
2
x
+
sin
2
x
)
(
cos
2
−
sin
2
x
)
=
cos
2
x
−
sin
2
x
=
cos
x
cos
x
−
sin
x
sin
x
=
cos
(
x
+
x
)
=
cos
2
x
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Answer:
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