Maths-
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Question

The side of triangle A B C are in A.P. (order being a comma blank b comma blank c) and satisfy fraction numerator 2 factorial over denominator 1 factorial 9 factorial end fraction plus fraction numerator 2 factorial over denominator 3 factorial 7 factorial end fraction plus fraction numerator 1 over denominator 5 factorial 5 factorial end fraction equals fraction numerator 8 to the power of a end exponent over denominator open parentheses 2 b close parentheses factorial blank end fraction comma blankthen the value of cos invisible function application A plus cos invisible function application B is

  1. fraction numerator 12 over denominator 7 end fraction  
  2. fraction numerator 13 over denominator 7 end fraction  
  3. fraction numerator 11 over denominator 7 end fraction  
  4. fraction numerator 10 over denominator 7 end fraction  

The correct answer is: fraction numerator 12 over denominator 7 end fraction


    fraction numerator 2 factorial over denominator 1 factorial 9 factorial end fraction plus fraction numerator 2 over denominator 3 factorial 7 factorial end fraction plus fraction numerator 1 over denominator 5 factorial 5 factorial end fraction equals fraction numerator 2 over denominator 10 factorial end fraction open parentheses blank to the power of 10 end exponent C subscript 1 end subscript close parentheses plus fraction numerator 2 over denominator 10 factorial end fraction open parentheses blank to the power of 10 end exponent C subscript 3 end subscript close parentheses plus fraction numerator 1 over denominator 10 factorial end fraction blank to the power of 10 end exponent C subscript 5 end subscript equals fraction numerator 1 over denominator 10 factorial end fraction open parentheses blank to the power of 10 end exponent C subscript 1 end subscript plus blank to the power of 10 end exponent C subscript 9 end subscript plus blank to the power of 10 end exponent C subscript 3 end subscript plus blank to the power of 10 end exponent C subscript 7 end subscript plus blank to the power of 10 end exponent C subscript 5 end subscript close parentheses
    equals fraction numerator 1 over denominator 10 factorial end fraction open parentheses 2 to the power of 10 minus 1 end exponent close parentheses equals fraction numerator 2 to the power of 9 end exponent over denominator 10 factorial end fraction equals fraction numerator 8 to the power of a end exponent over denominator open parentheses 2 b close parentheses factorial end fraction blank open parentheses g i v e n close parenthesesrightwards double arrow 3 a equals 9 comma blank 2 b equals 10 blank rightwards double arrow a equals 3 comma blank b equals 5
    Also,blank a comma blank b comma blank c blankare in A.P. blank rightwards double arrow c equals 7
    cos invisible function application A equals fraction numerator b to the power of 2 end exponent plus c to the power of 2 end exponent minus a to the power of 2 end exponent over denominator 2 b c end fraction equals fraction numerator 25 plus 49 minus 9 over denominator 2 cross times 5 cross times 7 end fraction equals fraction numerator 65 over denominator 2 cross times 5 cross times 7 end fraction equals fraction numerator 13 over denominator 14 end fraction
    cos invisible function application B equals fraction numerator a to the power of 2 end exponent plus c to the power of 2 end exponent minus b to the power of 2 end exponent over denominator 2 a c end fraction equals fraction numerator 9 plus 49 minus 25 over denominator 2 cross times 3 cross times 7 end fraction equals fraction numerator 11 over denominator 14 end fraction
    rightwards double arrow cos invisible function application A plus cos invisible function application B equals fraction numerator 13 plus 11 over denominator 14 end fraction equals fraction numerator 24 over denominator 14 end fraction equals fraction numerator 12 over denominator 7 end fraction

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