InterviewSolution
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InterviewSolution
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In triangle ABC, if `A - B = 120^(2) and R = 8r`, where R and r have their usual meaning, then cos C equalsA. `3//4`B. `2//3`C. `5//6`D. `7//8` |
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Answer» Correct Answer - D `R = 8r = 8 (4R sin.(A)/(2) sin.(B)/(2) sin.(C)/(2))` `:. 2 sin.(A)/(2) sin.(B)/(2) sin.(C)/(2) = (1)/(16)` or `(cos.(A -B)/(2) -cos.(A +B)/(2)) sin.(C)/(2) = (1)/(16)` or `sin.(C)/(2) ((1)/(2) - sin.(C)/(2)) = (1)/(16) rArr sin.(C)/(2) = (1)/(4)` or `cos C = 1 -2 sin^(2).(C)/(2) = 1 - (1)/(8) = (7)/(8)` |
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