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Prove that cos alpha cos (120^(@) + al...

Prove that
`cos alpha cos (120^(@) + alpha) cos (240^(@) + alpha) = 1/4 cos 3 alpha`

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Prove that, cos alpha + cos(120^(@) + alpha) + cos (120^(@) - alpha) = 0

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CHHAYA PUBLICATION-TRANSFORMATIONS OF SUMS AND PRODUCTS-Short Answer Type Questions
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  6. Find the value: sqrt3 cot20^(@) cot40^(@)cot80^(@)

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  13. If sin 2 alpha = 4 sin 2 beta, "show that", 5tan ( alpha -beta) = 3 ta...

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  14. If sin A = m sin B, "prove that" "tan" (A-B)/2 = (m-1)/(m+1) "tan" (A+...

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  16. If "cosec"A + secA = "cosec"B + sec B prove that "tan"(A+B)/2 = cot ...

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  17. If alpha,beta,gamma "are in A.P. show that" cot beta = (sin alpha - si...

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  18. If cot y =(sin(z+x))/(cos (z-x)-cos(z+x)),"show that" cot x , cot y "a...

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  19. If sinx + sin y = sqrt3 (cosy-cos x),"then show that" sin 3x+ sin 3y =...

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