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tmua.me Medium Set E Paper 2 · Q11

Paper 2Sequences & seriesNumber & counting

A sequence is defined by

u1=2,u2=1,un+2=3unfor every integer n≥1.u_1=2,\qquad u_2=1,\qquad u_{n+2}=3u_n\quad\text{for every integer }n\geq1.

What is the value of u1+u2+⋯+u20u_1+u_2+\cdots+u_{20}?

A310−12\dfrac{3^{10}-1}{2}
B310−13^{10}-1
C3(39−1)2\dfrac{3(3^9-1)}{2}
D320−13^{20}-1
E3(310−1)2\dfrac{3(3^{10}-1)}{2}

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