Question

find the sum of the first 13terms of the sequence -3, -1, 1, 3.....​

Answer 1

Answer:

117

Step-by-step explanation:

It is an A.P.

First term (a) = -3, Common Difference = 2

Sum of 13 terms = 13/2(-6 + (12)2) = 13(9) = 117

Answer 2

Answer: 117

Step-by-step explanation:

Here,  a = -3  and

           d = a₂ - a₁

               = -1 - (-3)

               = -1 + 3

               = 2

Hence, this forms an arithmetic progression (AP).

Sum of first 'n' terms of an AP = Sₙ = n/2 × [2a + (n-1)d]

∴Sum of first 13 terms = S₁₃ = 13/2 × [2×-3 + (13 - 1) × 2]

                                              =  13/2 ×  [ -6 + 12×2 ]

                                              =  13/2 × [ -6 + 24 }

                                              =  13/2 × 18

                                              =   13 × 9

                                              =   117

HOPE THIS HELPS.............