1.

the 9th term and 19th terms of a series in A.P.are respectively 35 and 75.find the series and it's 20th term.

Answer»

tn=a+(n-1)d35=a+(9-1)d35=a+8d. (1)Also,75=a+(19-1)d75=a+18d. (2)Subtracting 1 and 2,40=10dd=4a=75-18(4)a=3



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