Sum of Trigonometric Ratios in Terms of Their Product
If sinx + s...
Question
If sinx+siny=3(cosy−cosx), then the value of sin3x+sin3y=
A
−1
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B
1
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C
2
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D
0
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Solution
The correct option is D0 sinx+siny=3(cosy−cosx) ⇒sinx+3cosx=3cosy−siny...(1) Let 3=asinA and 1=acosA Therefore (1) is acosAsinx+asinAcosx=asinAcosy−acosAsiny
⇒sin(A+x)=sin(A−y)
A+x=A−y⇒x=−y Now sin3x+sin3y=sin3x+sin(−3x)=sin3x−sin3x=0