A geometric series has first term a a\,a and common ratio rrr. The second term of the series is 4 and the sum to infinity of the series is 25.
Show that 25r2−25r+4=025r^2 - 25r + 4 = 025r2−25r+4=0.
Find the two possible values of rrr.
Find the corresponding two possible values of aaa.
Show that the sum, SnS_nSn, of the first n n\,n terms of the series is given by
Sn=25(1−rn). S_n = 25(1 - r^n). Sn=25(1−rn).Given that r r\,r takes the larger of its two possible values, find the smallest value of n n\,n for which Sn S_n\,Sn exceeds 24.
Practise Edexcel A Level Old Maths Sequences and Series with exam-style questions for A Level Old Maths. 10 questions, matched to the Edexcel A Level Old Maths (9371) specification and written in Unit exams C1, C2, C3 and C4 plus two applied units (e.g. S1 and M1) style. Every question includes a full worked solution and mark scheme, so you can see where marks are awarded rather than just whether you got the answer right.