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NCERT Class XI Mathematics - Trigonometric Functions - Solutions

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Question : 33
Total: 61
cos9x−cos5x
sin17x−sin3x
 = -
sin2x
cos10x
Solution:  
We have, L.H.S =
cos9x−cos5x
sin17x−sin3x
=
−2sin(
9x+5x
2
)sin(
9x−5x
2
)
2sin(
17x−3x
2
)cos(
17x+3x
2
)
 =
−2sin7xsin2x
2sin7xcos10x
 =
−sin2x
cos10x
 = R.H.S.
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