Question

Find the sum of 5+8+11+....+89 terms using the formula

Answer 1

Answer:

SUM = 1363

Step-by-step explanation:

sequence is 5+8+11+....+89

here ,

first term, f₁ = 5

last term, fₙ = 89

common difference, d = 3

formula for last term = dn+(f-d)

                               = 3n+(5-3)

                               = 3n+2

we know last term is 89

∴  3n+2 = 89

   3n     = 89-2

   3n     = 87

     n     = 87/3

            = 29

    sum = n/2 x (first term + last term)

      S₂₉= 29/2 [ 5+89 ]

           = 29/2 X 94

           = 29 X 47

           = 1363