∑ 等差/等比数列求和Arithmetic & Geometric Series Calculator
计算等差数列和等比数列的第 n 项与前 n 项和，以及无穷等比级数的和。nth term and sum of the first n terms of arithmetic and geometric series, plus infinite geometric sums.
使用说明与常见问题How-to & FAQ
「等差/等比数列求和」是什么？What is the Arithmetic & Geometric Series Calculator?
计算等差数列和等比数列的第 n 项与前 n 项和，以及无穷等比级数的和。nth term and sum of the first n terms of arithmetic and geometric series, plus infinite geometric sums.
如何使用「等差/等比数列求和」？How do I use the Arithmetic & Geometric Series Calculator?
在「等差/等比数列求和」中，填写「类型」、「首项 a₁」、「公差 d / 公比 r」、「项数 n」等参数，结果会随输入实时计算并显示在下方。In the Arithmetic & Geometric Series Calculator: Fill in "Type", "First term a₁", "Difference d / ratio r", "Terms n"; results are recalculated instantly as you type.
计算精度如何？How precise are the results?
「等差/等比数列求和」使用 JavaScript 双精度浮点数（约 15–16 位有效数字）；极大或极小的数值可能存在精度误差。The Arithmetic & Geometric Series Calculator uses double-precision floating point (about 15–16 significant digits); very large or very small values may lose precision.
「等差/等比数列求和」免费吗？需要注册吗？Is the Arithmetic & Geometric Series Calculator free? Do I need an account?
「等差/等比数列求和」完全免费，无需注册或安装，打开网页即可使用，手机和电脑都能用；输入的内容只在你的浏览器本地处理。The Arithmetic & Geometric Series Calculator is completely free with no sign-up or install and works on phones and desktops; what you enter is processed only in your browser.