SPM 2017 Add Maths Paper 1, Question 8Progressions

Solved on video in English and Bahasa Melayu · 3 marks · Form 4, Progressions · 3:32 video

The question

It is given that the sum of the first n terms of an arithmetic progression is S_n = (n/2)[13 - 3n]. Find the n-th term.

[3 marks]

Step 1

Use T_n = S_n - S_(n-1).

Why this step

S_n adds every term up to T_n, while S_(n−1) stops just before it. Subtract them and only T_n is left, so we don't need a and d first.

4 more steps, each with the reason for it, in the full solution

Final answer

T_n = 8 − 3n

Where students lose marks

Watch out: expand S_(n−1) carefully and take the minus sign across every term of the second bracket. Slips here cost marks.

Watch every step of this question solved on video (3:32), with the reason behind each step and a box that checks your own answer.

No card. Every past-year question on video, in English and BM.