Trigonometric Identities Calculator

Calculate all trigonometric function values using Pythagorean, Double Angle, and Half Angle identities. Enter any known trig value and quadrant to find sin, cos, tan, csc, sec, cot with step-by-step solutions.

Free to useNo sign-up requiredUpdated Jan 2026

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Quick Examples

30° sin=0.5, Q1 45° cos, Q1 60° sin, Q1 225° tan=1, Q3 120° cos, Q2 330° sin, Q4

Known Function

Known Value

Quadrant

Q2Sin+

Q1All+

Q3Tan+

Q4Cos+

Identity Type

Precision

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About Trigonometric Identities Calculator

Welcome to the Trigonometric Identities Calculator, a comprehensive tool for calculating all trigonometric function values using fundamental identities. When you know one trig value (like $\sin(x)$ or $\cos(x)$) and the quadrant, this calculator finds all other values and applies various identity formulas with complete step-by-step solutions.

What This Calculator Does

Given a known trigonometric function value and the quadrant where the angle lies, this calculator:

Calculates all six basic trig functions: $\sin(x)$, $\cos(x)$, $\tan(x)$, $\csc(x)$, $\sec(x)$, $\cot(x)$
Applies Double Angle Formulas: Find $\sin(2x)$, $\cos(2x)$, and $\tan(2x)$
Applies Half Angle Formulas: Find $\sin(x/2)$, $\cos(x/2)$, and $\tan(x/2)$
Determines the exact angle: Both in degrees and radians
Verifies identities: Confirms the Pythagorean identity $\sin^2(x) + \cos^2(x) = 1$

Key Trigonometric Identities

Pythagorean Identities

$$\sin^2(x) + \cos^2(x) = 1$$
$$1 + \tan^2(x) = \sec^2(x)$$
$$1 + \cot^2(x) = \csc^2(x)$$

Double Angle Formulas

$$\sin(2x) = 2\sin(x)\cos(x)$$
$$\cos(2x) = \cos^2(x) - \sin^2(x) = 2\cos^2(x) - 1 = 1 - 2\sin^2(x)$$
$$\tan(2x) = \frac{2\tan(x)}{1 - \tan^2(x)}$$

Half Angle Formulas

$$\sin\left(\frac{x}{2}\right) = \pm\sqrt{\frac{1 - \cos(x)}{2}}$$
$$\cos\left(\frac{x}{2}\right) = \pm\sqrt{\frac{1 + \cos(x)}{2}}$$
$$\tan\left(\frac{x}{2}\right) = \frac{\sin(x)}{1 + \cos(x)} = \frac{1 - \cos(x)}{\sin(x)}$$

Understanding Quadrants (ASTC Rule)

The sign of each trigonometric function depends on which quadrant the angle is in. Remember the mnemonic "All Students Take Calculus" (ASTC):

Quadrant I (0° to 90°): All functions are positive
Quadrant II (90° to 180°): Only Sin (and csc) is positive
Quadrant III (180° to 270°): Only Tan (and cot) is positive
Quadrant IV (270° to 360°): Only Cos (and sec) is positive

Reciprocal Identities

$\csc(x) = \frac{1}{\sin(x)}$
$\sec(x) = \frac{1}{\cos(x)}$
$\cot(x) = \frac{1}{\tan(x)} = \frac{\cos(x)}{\sin(x)}$

How to Use This Calculator

Select the known function: Choose which trigonometric function value you know (sin, cos, tan, csc, sec, or cot).
Enter the known value: Input the numerical value. For sin and cos, this must be between -1 and 1. For csc and sec, the absolute value must be at least 1.
Select the quadrant: Choose which quadrant the angle x lies in. This determines the signs of other functions using the ASTC rule.
Choose identity type: Select which identities to apply (Pythagorean only, Double Angle, Half Angle, or All).
Set precision: Choose how many decimal places you want (1-100).
Click Calculate: View the complete results with step-by-step solutions and visual representation.

Frequently Asked Questions

What are trigonometric identities?

Trigonometric identities are equations involving trigonometric functions that are true for all values of the variables. The most fundamental is the Pythagorean identity: $\sin^2(x) + \cos^2(x) = 1$. Other important identities include double angle formulas, half angle formulas, sum and difference formulas, and reciprocal identities.

How do I find all trig values from one known value?

To find all six trigonometric values from one known value: 1) Use the Pythagorean identity to find sin or cos. 2) Determine the correct sign based on the quadrant using ASTC rule. 3) Calculate the remaining functions using reciprocal and quotient identities.

What is the ASTC rule for quadrants?

ASTC stands for All-Sin-Tan-Cos, a mnemonic to remember which trig functions are positive in each quadrant. In Quadrant I, All functions are positive. In Quadrant II, only Sin (and csc) is positive. In Quadrant III, only Tan (and cot) is positive. In Quadrant IV, only Cos (and sec) is positive.

What are double angle formulas?

Double angle formulas express trigonometric functions of 2x in terms of functions of x. The main formulas are: $\sin(2x) = 2\sin(x)\cos(x)$, $\cos(2x) = \cos^2(x) - \sin^2(x)$, and $\tan(2x) = \frac{2\tan(x)}{1 - \tan^2(x)}$.

What are half angle formulas?

Half angle formulas express trigonometric functions of x/2 in terms of cos(x). The formulas are: $\sin(x/2) = \pm\sqrt{\frac{1-\cos(x)}{2}}$, $\cos(x/2) = \pm\sqrt{\frac{1+\cos(x)}{2}}$, and $\tan(x/2) = \frac{\sin(x)}{1+\cos(x)}$. The sign depends on which quadrant x/2 falls in.

Applications

Education: Learn and verify trigonometric identities for math courses
Engineering: Signal processing, wave analysis, and circuit design
Physics: Harmonic motion, oscillation, and wave mechanics
Navigation: Calculating angles, distances, and bearings
Computer Graphics: Rotation matrices and transformation calculations

Additional Resources

Reference this content, page, or tool as:

"Trigonometric Identities Calculator" at https://MiniWebtool.com/trigonometric-identities-calculator/ from MiniWebtool, https://MiniWebtool.com/

by miniwebtool team. Updated: Jan 13, 2026

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