SPM 2018 Add Maths Paper 1, Question 14Progressions

Solved on video in English · 4 marks · Form 4, Progressions · 4:08 video

The question

It is given that p, 2 and q are the first three terms of a geometric progression. Express in terms of q (a) the first term and the common ratio of the progression, (b) the sum to infinity of the progression.

[4 marks]

SPM 2018 Add Maths Paper 1, Question 14: the question as drawn in Eduly's video4:08

Step 1

In a geometric progression the ratio between consecutive terms is constant, so the common ratio r = (2nd term)/(1st term) = (3rd term)/(2nd term).

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

Final answer

First term = 4/q; common ratio = q/2; S∞ = 8/[q(2 − q)]

Where students lose marks

Watch out: give r in terms of q (q/2, not 2/p), and use a/(1 − r), not the finite sum formula.

Watch every step of this question solved on video (4:08), with the reason behind each step and a box that checks your own answer.

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