Cos2A _ SIN2A =1-2sin2a
1+tan2A 1+COTAN2A
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Answer:
cos
(
2
a
)
=
1
−
2
sin
2
a
Use cosine sum identity :
cos
(
a
+
a
)
=
1
−
2
sin
2
a
cos
a
cos
a
−
sin
a
sin
a
=
1
−
2
sin
2
a
cos
2
a
−
sin
2
a
=
1
−
2
sin
2
a
Apply modified pythagorean identity :
cos
2
x
=
1
−
sin
2
x
(
1
−
sin
2
a
)
−
sin
2
a
=
1
−
2
sin
2
a
1
−
2
sin
2
a
=
1
−
2
sin
2
a
Step-by-step explanation:
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