Question

the frist and the last of an AP are 17 and 350 if the common differene is 9 how many term are there and what is thier sum ?

Answer 1

Heya !!




Common difference ( D ) = 9




First term ( A ) = 17


Last term ( Tn ) = 350



A + ( N - 1 ) × D = 350




17 + ( n - 1 ) × 9 = 350



17 + 9N - 9 = 350




9N + 8 = 350



9n = 350-8



9n = 342


N = 342/9 = 38.



Number of terms = 38.




Sn = N/2 × [ 2A + ( n - 1 ) × D ]



S38 = 38/2 × [ 2 × 17 + ( 38 - 1 ) × 9 ]




=> 19 × ( 34 + 333 )



=> 19 × 367



=> 6973 .

Answer 2

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