Trig Identity Checker
Trigonometry
Pick angles A, B; verify sin(A+B), cos(A+B), etc., numerically.
Angles
Each row shows the LHS computed two ways: direct evaluation vs the addition / double-angle identity. The absolute difference is ~0 (limited only by floating-point precision).
Verifications
| Expr | Direct | Identity | |Δ| |
|---|---|---|---|
| sin(A+B) | 0.96592583 | 0.96592583 | 0 |
| cos(A+B) | 0.25881905 | 0.25881905 | 0 |
| sin(A−B) | -0.25881905 | -0.25881905 | 0 |
| cos(A−B) | 0.96592583 | 0.96592583 | 0 |
| sin 2A | 0.8660254 | 0.8660254 | 0 |
| cos 2A | 0.5 | 0.5 | 0 |
Frequently asked questions
▶What does the Trig Identity Checker do?
The Trig Identity Checker is an interactive trigonometry lab where you change inputs and the answers update live, helping you build intuition without doing the arithmetic by hand.
▶Who should use the Trig Identity Checker?
Students from primary to senior secondary classes, parents helping with homework, and anyone revising trigonometry can use this lab to check answers and explore "what-if" scenarios.
▶Is the Trig Identity Checker free to use?
Yes. Every lab on math.suparnpatra.com is free and runs entirely in your browser : nothing is sent to a server.
▶Does the Trig Identity Checker work offline?
Once the page is loaded, all calculations run locally in JavaScript, so you can keep using it even on a flaky connection.
▶How accurate are the results?
Results use standard JavaScript double-precision arithmetic and the textbook formula for trigonometry. We never display scientific notation : numbers are shown as ordinary decimals you can read at a glance.