Question

Sum of first n term of an sequence is 3nsq-6n
find first term and common difference

Answer 1

Answer:

First term = -3

common difference = 6

Explanation:

first term = sum of first itself = 3×1² - 6×1

                                           = 3-6 = -3

let second term be a,

sum of first two terms = -3+a = 3×2² - 6×2

                                    -3+a = 3×4 -12

                                    -3+a = 12-12

                                    -3+a = 0

                                         a = 3

that is, second term = 3 and first term = -3

then, common difference = second term - first term

                                       = 3- -3

                                       = 3+3

                                       = 6

                                      OR

If sum of first n terms of a sequence is given,

   common difference = 2x coefficient of n²

                   [here common difference = 2x 3 =6]

   first term sum of all coefficients, ie, coefficient of x² & x

                   [here first term = 3+-6 =-3]

       Hope this answer will help u.......