The terms, unu_nun, of a periodic sequence are defined by
u1=5andun+1=10un u_1 = 5 \quad \text{and} \quad u_{n+1} = \frac{10}{u_n} u1=5andun+1=un10Find u2u_2u2, u3u_3u3 and u4u_4u4.
State the period of the sequence.
Find the value of ∑n=151un\sum_{n=1}^{51} u_n∑n=151un.
308 exam-style questions on OCR A Level Maths 1.4 Sequences and Series, covering 1.4.1 Binomial expansion for positive integer n, 1.4.2 Link to binomial probabilities, 1.4.3 Binomial expansion for rational n (A-level only), 1.4.4 Validity of the expansion (A-level only), 1.4.5 Sequences (A-level only), 1.4.6 Increasing, decreasing and periodic sequences (A-level only), 1.4.7 Sigma notation (A-level only), 1.4.8 Arithmetic sequences and series (A-level only), 1.4.9 Geometric sequences and series (A-level only), 1.4.10 Sum to infinity of a geometric series (A-level only), and 1.4.11 Modelling with sequences and series (A-level only). Each one has a worked solution and a mark scheme showing where the marks go.