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1 Pure Mathematics

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Question 470

A sequence a1,a2,a3,… a_1, a_2, a_3, \dots\,a1​,a2​,a3​,… is defined by

an+1=k−anana_{n+1} = \dfrac{k - a_n}{a_n}an+1​=an​k−an​​

where k k\,k is a constant. The sequence is periodic of order 3 and a1=3a_1 = 3a1​=3.

a.

Show that k2−11k−12=0k^2 - 11k - 12 = 0k2−11k−12=0.

[3]
b.

For this sequence, explain why k≠12k \neq 12k=12.

[1]
c.

Find the value of ∑r=1100ar\sum_{r=1}^{100} a_r∑r=1100​ar​.

[3]
Markscheme

1 Pure Mathematics Questions

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