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plss answer  fast  experts 11. Sides ofa triangle are a,b,c and its inradius is R. Prove that area of this triangle is abc 4R Answer to any 7 of the questions from 12 to 21 (7x4=28 score) Rth 0th

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Note : This question involves concept of higher grade but still providing the solution.Solution:Using sine rule:asinA=bsinB=csinC=2RNow from the figure BD when joined becomes diameter  and angle in a semicircle is 90°.BCD=90°Also, BO=R and BD=2Rand BDC=A  angles in the same segment are equal.Now in BCDsinD=BCBD=a2RSo, asinA=2RAlso, area of =12ab sinC  ...1and csinC=2Rc2R=sinCSo, 1 becomesAlso, area of =12ab c2R=abc4RHence Proved.


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