Trình tính biểu thức toán

(Tài liệu bằng tiếng Anh)

What it does

Evaluates a math expression as you type and shows the result in large type that scales with its length. The vocabulary is arithmetic, powers, and the common functions and constants: sqrt, sin, cos, tan, log, pi, e, and parentheses. Input is constrained to math-safe characters and evaluated locally in your browser. Nothing is transmitted.

How to use it

1. Type an expression into the large centered field. It evaluates on each keystroke.
2. Or tap an example chip: 2 * (3 + 4) / 5, sqrt(16) + 2^10, sin(pi / 6), log(e^3) + 7, 2^16 - 1.
3. The result renders below, sized to fit. Clear empties the input, and the result leaves with it.
4. Copy share link encodes the expression in the URL (?t=...).

Examples

Expression	Result	Note
2 * (3 + 4) / 5	2.8	parentheses first
sqrt(16) + 2^10	1028	4 + 1,024
sin(pi / 6)	0.49999999999999994	the honest floating-point answer, not 0.5
2^16 - 1	65535	the largest 16-bit unsigned value

The sin(pi / 6) result deserves its note. pi cannot be stored exactly in binary floating point, so the sine comes out one step off the tidy 0.5. That is correct IEEE 754 behavior, and the tool prints it rather than rounding behind your back.

How expression evaluation works

Evaluating a string typed by a stranger is the classic injection problem: JavaScript’s eval would run code, not math. This tool never calls eval. The input passes a guard first, and only a string made purely of math characters reaches the evaluator:

Allowed	Blocked
digits, letters, spaces	quotes and backticks
+ - * / % ^ ! ( ) , . < >	brackets, braces, semicolons
expressions up to 200 characters	keywords like import, eval, function

Letters are needed for sqrt and pi, so they pass the character check, but a word sequence that names code instead of math is rejected outright. Anything outside the vocabulary fails before evaluation, which also covers shared links: an expression planted in a ?t= URL dies at the same guard.

Good to know

• log is natural: in this evaluator log means the natural logarithm (base e), so log(e) is 1. There is no separate ln function; an expression using one shows “Could not evaluate”.
• No side effects: an expression can only produce a value. It cannot reach the page, the network, or your files.
• Private: evaluation runs locally; nothing is transmitted.
• Related tools: Percentage Calculator, Statistics Calculator, Number Base Converter.