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the answer to this question is -2. cant the answer be ‘independent of alpha’?

the answer to this question is -2. cant the answer be ‘independent of alpha’?

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Grade:10

1 Answers

Vikas TU
14149 Points
7 years ago
i can provide u a hint and then u can do it  by yourself.
simply apply formulae: 

cos(A+B) + cos(A-B) = 2cosAcosB

for those two cosine terms,
U WOULD get cos2alpha and cos120
write cos2alpha in sin term and then solve u would get -2 as the answer.

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