Scientific Calculator · Practical guide
How to Use Sin, Cos, and Tan on a Calculator
One toggle decides whether your trig answer is right: DEG or RAD. Set it first, then type the function and the angle.
At a glance
The Short Answer
Set the DEG/RAD toggle first, then type the function and the angle: sin(30) returns 0.500000 in DEG mode. The single most common trig mistake is being in the wrong angle mode — in RAD mode the same entry returns -0.988032, the sine of 30 radians instead of 30 degrees.
Interactive tool
Scientific Calculator
Enter your own values, then compare the result with the examples below.
History
DEG or RAD: Which Do You Need?
Degrees split a circle into 360 parts; radians split it into 2π ≈ 6.283. Use degrees for geometry homework, bearings, and angles you would measure with a protractor. Use radians for calculus, physics, and any formula involving π. Whenever a trig answer looks wrong, check the toggle before anything else.
Common Values to Check Your Work
| You Type (DEG mode) | Displayed | Exact Value |
|---|---|---|
| sin(30) | 0.500000 | 1/2 |
| cos(60) | 0.500000 | 1/2 |
| tan(45) | 1.000000 | 1 |
| sin(90) | 1.000000 | 1 |
| cos(0) | 1.000000 | 1 |
If your results match this table, your mode and entries are correct. If sin(30) shows -0.988032, you are in RAD mode.
SOH-CAH-TOA in Practice
For a right triangle, sin = opposite/hypotenuse, cos = adjacent/hypotenuse, tan = opposite/adjacent. Example: a ramp rises 3 feet over a 5-foot horizontal run, so tan(angle) = 3/5 = 0.6. This calculator has no inverse-trig keys, so to recover the angle you would need arctan(0.6) ≈ 31° from another source — but verifying the forward direction is instant: tan(31) in DEG mode displays about 0.600861, confirming the angle.
Frequently Asked Questions
Why does sin(30) equal 0.5 on some calculators and -0.988 on others?
Angle mode. 0.500000 is the sine of 30 degrees; -0.988032 is the sine of 30 radians. Switch the DEG/RAD toggle to match your problem.
Does this calculator have inverse sin, cos, or tan?
No — the key set covers the forward trig functions only. To solve for an angle from a ratio, use an arcsin/arctan resource, then verify the result here.
What happens at tan(90)?
Tangent is undefined at 90° because cosine is zero in the denominator. The calculator returns an extremely large number rather than an error — treat that as undefined.
How do I enter an angle in radians?
Switch the toggle to RAD and type the value directly — sin(3.14159) returns approximately 0. You can also build the angle with the π key, such as sin(pi/2) = 1.000000.