Edexcel Mathematics October 2020 · Paper 2 · Question 15 · ExamRizz

ExamRizzEdexcel MathematicsMathematics

October 2020 · Paper 2 · Question 15 · 8 marks

15. In this question you must show all stages of your working. Solutions r elying entirely on calculator technology are not acceptable. A geometric series has common ratio r and first term a. Given r ≠ 1 and a ≠ 0 (a) prove that Sn = ar rn1 1−() − (4) Given also that S10 is four times S5 (b) find the exact value of r. (4) 47 48 49