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Mathematics
Mathematics
Problem
Prove that,
(
cos
A
+
cos
B
)
2
+
(
sin
A
+
sin
B
)
2
=
4
cos
2
A
−
B
2
.
(\cos A + \cos B)^2 + (\sin A + \sin B)^2 = 4 \cos^2 \frac{A-B}{2}.
(
cos
A
+
cos
B
)
2
+
(
sin
A
+
sin
B
)
2
=
4
cos
2
2
A
−
B
.
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