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10 questions from this quiz
Common difference
an=a1+(n−1)da_n = a_1 + (n-1)dan=a1+(n−1)d
Sn=n2(2a1+(n−1)d)S_n = \frac{n}{2}(2a_1 + (n-1)d)Sn=2n(2a1+(n−1)d)
Multiplying by a constant
an=a1rn−1a_n = a_1 r^{n-1}an=a1rn−1
Sn=a1(1−rn)1−rS_n = \frac{a_1(1-r^n)}{1-r}Sn=1−ra1(1−rn)
∣r∣<1|r| < 1∣r∣<1
6400
90+10n90 + 10n90+10n
£42,500
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