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Problems
Mathematics
Mathematics
Problem
Express
cos
5
x
cos
3
x
\cos5x\,\cos3x
cos
5
x
cos
3
x
as a sum and choose the correct equivalent form. a)
1
2
(
cos
8
x
−
cos
2
x
)
\dfrac12\bigl(\cos8x-\cos2x\bigr)
2
1
(
cos
8
x
−
cos
2
x
)
b)
1
2
(
cos
8
x
+
sin
2
x
)
\dfrac12\bigl(\cos8x+\sin2x\bigr)
2
1
(
cos
8
x
+
sin
2
x
)
c)
1
2
(
cos
8
x
+
cos
2
x
)
\dfrac12\bigl(\cos8x+\cos2x\bigr)
2
1
(
cos
8
x
+
cos
2
x
)
d)
1
2
(
sin
8
x
+
sin
2
x
)
\dfrac12\bigl(\sin8x+\sin2x\bigr)
2
1
(
sin
8
x
+
sin
2
x
)
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