1.

Let `A and B` denote the statements `A : cos alpha + cos beta + cos gamma =0` `B : sin alpha + siin beta + sin gamma = 0` If `cos(beta - gamma) + cos (gamma -alpha) + cos (alpha -beta) = - (3)/(2)`, thenA. `A` is true and `B` is false.B. `A` is false and `B` is true.C. Both `A and B` are true.D. Both `A and B` are false.

Answer» Correct Answer - C
` cos (beta -gamma) +cos (gamma - alpha ) + cos (alphea - beta) =-(3)/(2)`
`rArr 2 [cos (beta -gamma) +cos (gamma -alpha ) + cos (alpha - beta)] + 3 =0`
`rArr 2 [cos (beta -gamma ) + cos (gamma -alpha) + cos (alpha -beta)] + sin ^(2) alpha + cos ^(2) alpha + sin ^(2) beta + cos ^(2) beta + sin ^(2) gamma + cos ^(2) gamma =0`
`rArr (sin alpha + sin beta + sin gamma)^(2) + ( cos alpha + cos beta + cos gamma)^(2) =0`
`rArr cos alpha + cos beta + cos gamma =0`
and `sin alpha + sin beta + sin gamma =0`


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