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Question
Mathematics
cos 4 x cos 8 x- cos 5 x cos 9 x=0 if
Q.
cos
4
x
cos
8
x
−
cos
5
x
cos
9
x
=
0
if
35
175
Trigonometric Functions
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A
cos
12
x
=
cos
14
x
33%
B
sin
13
x
=
0
4%
C
sin
x
=
0
8%
D
all of these
54%
Solution:
cos
4
x
cos
8
x
−
cos
5
x
cos
9
x
=
0
⇒
2
cos
4
x
cos
8
x
=
2
cos
5
x
cos
9
x
⇒
cos
12
x
+
cos
4
x
=
cos
14
x
+
cos
4
x
⇒
14
x
=
2
nπ
±
(
12
x
)
⇒
2
x
=
2
nπ
or
26
x
=
2
nπ
⇒
x
=
nπ
or
13
nπ
∴
sin
x
=
0
or
sin
13
x
=
0