Q9 (Approximation of π) (a)
Show that 1/1 + t2 = 1 − t2 + t4 −
... + (−1)n−1 t 2n−2 + (−1)n
t2n /1 + t2 for all t ∈ R and n ∈ N.
(b) Integrate both side in (a), show that tan−1 (x) = x − x3/3 + x5 /5 − ... + (−1)n−1x 2n−1/ 2n − 1 + Z x 0 (−1)n t2n /1 + t2 dt.
(c) Show that tan−1 (x) − ( x − x3 /3 + x5 /5 − ... + (−1)n−1x 2n−1 /2n − 1) ≤ x 2n+1 /2n + 1 .
(d) Show that tan−1 1/2 + tan−1 1/3 = π/4
(e) Show that π/4 − ((1/2 + 1/3 ) − 1/3(1/23 + 1/33 ) + 1/5 (1/25 + 1/35 ) − ... + (−1)n−1 /2n − 1 ( 1/2 2n−1 + 1/ 32n−1 )) ≤ 1 /n · 2 2n−1




Q9 (Approximation of π) (a) Show that 1/1 + t2 = 1 − t2 + t4 − ... + (−1)n−1 t 2n−2 + (−1)n t2n /1 + t2 for all t ∈ R and n ∈ N. (b) Integrate both side in (a), show that tan−1 (x) = x − x3/3 + x5 /5...