IF RATIO OF SUM OF TWO AP'S ARE 7N+2:3N+1.THEN FIND RATIO OF 17TH TERM? PLEASE EXPLAIN IN DETAIL?AND WHEN WILL TOPPER LIVE COURSES WILL START FOR CBSE CLASS 10?

Asked by abinash.gupta003 | 5th Jul, 2017, 08:15: AM

Expert Answer:

begin mathsize 16px style Let space straight a subscript 1 comma space straight a apostrophe subscript 1 space be space the space first space terms space and space straight d subscript 1 comma space straight d apostrophe subscript 1 space the space common space differences space of space the space two space straight A greater than straight P. straight s
Then comma space sum space of space their space straight n space terms space are space given space by
straight S subscript straight n equals straight n over 2 left square bracket 2 straight a subscript 1 plus left parenthesis straight n minus 1 right parenthesis straight d subscript 1 right square bracket space and space straight S apostrophe subscript straight n equals straight n over 2 left square bracket 2 straight a apostrophe subscript 1 plus left parenthesis straight n minus 1 right parenthesis straight d apostrophe subscript 1 right square bracket
fraction numerator straight S subscript straight n over denominator straight S apostrophe subscript straight n end fraction equals fraction numerator 7 straight n plus 2 over denominator 3 straight n plus 1 end fraction
rightwards double arrow fraction numerator straight n over 2 left square bracket 2 straight a subscript 1 plus left parenthesis straight n minus 1 right parenthesis straight d subscript 1 right square bracket space over denominator straight n over 2 left square bracket 2 straight a apostrophe subscript 1 plus left parenthesis straight n minus 1 right parenthesis straight d apostrophe subscript 1 right square bracket end fraction equals fraction numerator 7 straight n plus 2 over denominator 3 straight n plus 1 end fraction
rightwards double arrow fraction numerator 2 straight a subscript 1 plus left parenthesis straight n minus 1 right parenthesis straight d subscript 1 space over denominator 2 straight a apostrophe subscript 1 plus left parenthesis straight n minus 1 right parenthesis straight d apostrophe subscript 1 end fraction equals fraction numerator 7 straight n plus 2 over denominator 3 straight n plus 1 end fraction
To space find space the space ratio space of space their space 17 th space terms comma space we space replace space straight n space by space 17.
rightwards double arrow fraction numerator 2 straight a subscript 1 plus 16 straight d subscript 1 space over denominator 2 straight a apostrophe subscript 1 plus 16 straight d apostrophe subscript 1 end fraction equals fraction numerator 7 cross times 17 plus 2 over denominator 3 cross times 17 plus 1 end fraction
rightwards double arrow fraction numerator straight a subscript 17 space over denominator straight a apostrophe subscript 17 end fraction equals 121 over 52 end style
 
We are starting Topper Live Classes for CBSE Class 10 from 17th July.

Answered by Rashmi Khot | 5th Jul, 2017, 09:10: AM