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Mathematics
Mathematics
Problem
Prove that
sin
(
x
+
y
)
sin
(
x
−
y
)
=
cos
2
y
−
cos
2
x
2
\displaystyle \sin(x+y)\sin(x-y) = \frac{\cos 2y - \cos 2x}{2}
sin
(
x
+
y
)
sin
(
x
−
y
)
=
2
cos
2
y
−
cos
2
x
.
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