1997+199.7+19.97+1.997+0.1997+0.01997怎么简便计算?
问题描述：
1997+199.7+19.97+1.997+0.1997+0.01997怎么简便计算?
答
等比数列前n项和公式：Sn = a(1 - q^n)/(1 - q)其中,a为首项,q为公比此处,a = 1997,q = 1/10,n = 6∴Sn = 1997[1 - (1/10)^6]/[1 - (1/10)] = 1997×(999999/1000000)÷(9/10) = 1997×111111/100000 = 2218.88667...