Question

sum each of following series 21 + 24 + 27 so on +81

Answer 1

here is your answer
hope it's help you
answer is 1071

Answer 2

HEY THERE!!


Question;-

Sum of the following 21 + 24 + 27 +..... +81



Method of Solution;-

Let to be first term'a' and it's CommOn difference'd' and also it's last term 'l'.


According to the Question must be we find Number of terms in the Given Arithmetic Sequence or Progression.

Using Formula of Arithmetic Sequence or Progression

Tn=a+(n-1)d

here,

a=21

d=3


l=81

Considering on Formula;-

Tn=a+(n-1)d

81=21+(n-1)3

81=21+3n-3

81=21-3+3n

81=18+3n

81-18=3n

=> 63=3n

=> n=63/3


=> n=21


According to the Question must be find Sum of terms of Following given Arithmetic Sequence or Progression Equation!-

Sn=n/2(a+l)

=> 21/2(21+81)

=> 21/2(102)

=> 21×51

=>1071

°•° Sn=1071


Hence, Sum of the following 21 + 24 + 27 +..... +81 = 1071