cos4a+sin4a=1-2cos2asin2a
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Answer:
sin
4
A+cos
4
A
We have (a
2
+b
2
)
2
=a
4
+b
4
+2a
2
b
2
⇒a
4
+b
4
=(a
2
+b
2
)
2
−2a
2
b
2
Take a=sinA and b=cosA we get
sin
4
A+cos
4
A=(sin
2
A+cos
2
A)
2
−2sin
2
Acos
2
A
=1−2sin
2
Acos
2
A proved.
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