>1656年,沃里斯(Wais证明 44 e 2k 2 2 2k-12k+1 取k=10 z≈).(22 2020 3.067702 13八(35 192l 取k=20 元≈ 2(3(3(3,#) 3.1035163.067702 21 20 19 20 5 4 3 4 3 2 1 2 2  =                         3.103516 4 1 4 0 3 9 4 0 5 4 3 4 3 2 1 2 2  =                         取 k = 20 取 k = 10 ➢ 1656年，沃里斯(Wallis)证明   =       +  − =                      =   1 2 1 2 2 1 2 2 7 6 5 6 5 4 3 4 3 2 1 2 2 k k k k k  