19N.2.AHL.TZ0.H_1

pestleMathematicsAAHLPaper 219N· sl-1-3-geometric-sequences-and-seriessource ↗

A geometric sequence has ${u_4} = - 70$ and ${u_7} = 8.75$ . Find the second term of the sequence.

Markscheme / solution

${u_1}{r^3} = - 70$ , ${u_1}{r^6} = 8.75$ (M1)

${r^3} = \frac{{8.75}}{{ - 70}} = - 0.125$ (A1)

$\Rightarrow r = - 0.5$ (A1)

valid attempt to find ${u_2}$ (M1)

for example: ${u_1} = \frac{{ - 70}}{{ - 0.125}} = 560$

${u_2} = 560 \times - 0.5$

$= - 280$ A1

[5 marks]

Examiners’ report

[N/A]