A-LevelMathematicsSeries9709/12 · Oct/Nov 2022 · Q25 Marks
The first, second and third terms of an arithmetic progression are a, 2a and a² respectively, where a is a positive constant. Find the sum of the first 50 terms of the progression.
- The first, second and third terms of an arithmetic progression are a, 2a and a² respectively, where a is a positive constant. Find the sum of the first 50 terms of the progression.[5]
Mark scheme
Marking points from the official mark scheme (Oct/Nov 2022). The mark or mark type is shown in brackets.
- B1 OE. An unsimplified correct equation in a or d only, e.g. a² + a = 4a. Can be implied by correct values for a or d. 2a - a = a² - 2a
- B1 Condone 'extra' solution of a = 0 or d = 0. a=3 or d=3
- B1 SOI. a = 3 and d = 3
- M1 May be done using 50th term (=150). Their a and d must be numerical. S₅₀ = 50/2 (2 × their a + 49 × their d)
- A1 ISW. 3825
- SC B2 for 1275a or 1275d
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