A-LevelMathematicsSeries9709/12 · Oct/Nov 2020 · Q25 Marks
The first, second and third terms of a geometric progression are 2p + 6, −2p and p + 2 respectively, where p is positive. Find the sum to infinity of the progression.
- (a)The first, second and third terms of a geometric progression are 2p + 6, −2p and p + 2 respectively, where p is positive. Find the sum to infinity of the progression.[5]
Mark scheme
Marking points from the official mark scheme (Oct/Nov 2020). The mark or mark type is shown in brackets.
- [M1] OE. Using “a, b, c then b² = ac” or a =2p+6, ar = -2p and ar² = p + 2 to form a correct relationship in terms of p only
- [A1] (2p²-10p-12 = 0) p = 6
- [A1] a = 18 and r = -2/3
- [M1] Correct formula used with their values for a and r, |r| < 1 Both a & r from the same value of p.
- [A1] (S∞ = )10.8 OE. A0 if an extra solution given
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