- (a) Both π/4 and the expression in brackets yield 0.7853981634, which is accurate to ten
decimal places.
(b)
(c) this agrees with the value of to four decimal places.
(d) The seriesconverges very slowly. Example 56 evaluated the sum of 60 terms of the series for π (which
equals 4 tan−1 1). To four decimal places, we get π = 3.1249, which yields 0.7812 for π/4—not
accurate even to two decimal places.