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In triangle ABC, `b^(2) sin 2C + c^(2) sin 2B = 2bc` where `b = 20, c = 21`, then inradius =A. 4B. 6C. 8D. 9 |
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Answer» Correct Answer - B `b^(2) sin 2C + c^(2) sin 2B = 2bc` `rArr b^(2) (2 sin C cos C) + c^(2) (2 sin B cos B) = 2bc` `rArr b^(2) (c cos C) + c^(2) (b cos B) = 2Rbc` `rArr b cos C + c cos B = 2R` `rArr a = 2R` `rArr A = 90^(@)` `:. a^(2) = b^(2) + c^(2) = 400 + 441 = 841` `rarr a = 29` Now, `r = (2Delta)/(2s) = (20 xx 21)/(20 + 21 + 29) = (20 xx 21)/(70) = 6` |
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