Page 5 - LN
P. 5

Find the number of terms in each of the following APs:



               (i) 7,13,19....,205     (ii) 18,  ,13,...−47


               Solution

                   (i)  7,13,19....,205

                          First term = a =7

                          Common difference = d = 13 - 7 = 19 - 13 = 6


                          a n=205


                          Using formula a n=a+(n−1)d, to find nth term of arithmetic progression, we
                          get



                          205= 7+(n−1)6 = 7+6n−6

                          ⇒205 = 6n+1




                          ⇒204 = 6n




                          ⇒n=       =34






                          Therefore, there are 34 terms in the given arithmetic progression.


                   (ii) 18,    ,13,...−47








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