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If `cos^(-1) alpha + cos^(-1) beta + cos^(-1) gamma = 3pi`, then `alpha (beta + gamma) + beta(gamma + alpha) + gamma(alpha + beta)` equal to |
Answer» Correct Answer - C We have, `cos^(-1) alpha + cos^(-1) beta + cos^(-1) gamma = 3 pi` We know that `0 le cos^(-1) x le pi` `rArr cos^(-1) alpha + cos^(-1) beta + cos^(-1) gamma = 3 pi` If and only if, `cos^(-1) alpha + cos^(-1) beta + cos^(-1) gamma = pi` `rArr cos pi = alpha = beta = gamma` `rArr -1 = alpha = beta = gamma` `rArr alpha = beta = gamma = - 1` `:. alpha(beta + gamma) + beta(gamma + alpha) + gamma (alpha + beta)` `= - 1 (-1-1)-1(-1-1)-1(-1-1)` `= 2+2+2 = 6` |
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