The value of 2 cos-13cos9 -13-cos3 -13-cos5 -13 is

The correct option is B 02cosπ13cos9π13+cos3π13+cos5π13 = cos10π13 +cos8π13+cos3π13+cos5π13 nbsp;= cos(π 3π13)+cos(π 5π13)+cos3π13+cos5π13 = cos3π13 c ...

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Standard XII

Mathematics

Sin(A+B)Sin(A-B)

The value of ...

Question

The value of $2 cos \frac{π}{13} cos \frac{9 π}{13} + cos \frac{3 π}{13} + cos \frac{5 π}{13}$ is

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\frac{1}{2}

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Solution

The correct option is B $0$
$2 cos \frac{π}{13} cos \frac{9 π}{13} + cos \frac{3 π}{13} + cos \frac{5 π}{13} = cos \frac{10 π}{13} + cos \frac{8 π}{13} + cos \frac{3 π}{13} + cos \frac{5 π}{13} = cos (π - \frac{3 π}{13}) + cos (π - \frac{5 π}{13}) + cos \frac{3 π}{13} + cos \frac{5 π}{13} = - cos \frac{3 π}{13} - cos \frac{5 π}{13} + cos \frac{3 π}{13} + cos \frac{5 π}{13} (∵ cos (π - θ) = - cos θ) = 0$

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Similar questions

Q. Value of :

2 cos \frac{π}{13} cos \frac{9 π}{13} + cos \frac{3 π}{13} + cos \frac{5 π}{13}

$2 c o s \frac{π}{13} c o s \frac{9 π}{13} + c o s \frac{3 π}{13} + c o s \frac{5 π}{13} =$

2 cos \frac{π}{13} cos \frac{9 π}{13} + cos \frac{3 π}{13} + cos \frac{5 π}{13}

is equal to

Q. Prove that:

2 c o s \frac{π}{13} c o s \frac{9 π}{13} + c o s \frac{3 π}{13} + c o s \frac{5 π}{13} = 0

Q. Prove that

2 cos \frac{π}{13} cos \frac{9 π}{13} + cos \frac{3 π}{13} + cos \frac{5 π}{13} = 0

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The value of 2cosπ13cos9π13+cos3π13+cos5π13 is

The correct option is B 02cosπ13cos9π13+cos3π13+cos5π13=cos10π13+cos8π13+cos3π13+cos5π13=cos(π−3π13)+cos(π−5π13)+cos3π13+cos5π13=−cos3π13−cos5π13+cos3π13+cos5π13(∵cos(π−θ)=−cosθ)=0

The value of $2 cos \frac{π}{13} cos \frac{9 π}{13} + cos \frac{3 π}{13} + cos \frac{5 π}{13}$ is