Pythagorean Theorem Calculator

Find the length of the hypotenuse or any missing leg of a right triangle. Enter two known sides to get the step-by-step solution.

Understanding the Pythagorean Theorem

The Pythagorean Theorem is a fundamental principle in Euclidean geometry that establishes a fixed mathematical relationship among the three sides of a right-angled triangle. Formulated by the ancient Greek mathematician Pythagoras, this theorem proves that the square of the longest side (the hypotenuse) is precisely equal to the sum of the squares of the other two shorter sides (the legs).

The Core Formula: \( a^2 + b^2 = c^2 \)

To utilize this theorem correctly, you must first assign the appropriate variables to the correct sides of your triangle:

Solving for a Missing Hypotenuse (\( c \))

If you are given the lengths of both legs (\( a \) and \( b \)) and need to find the hypotenuse (\( c \)), the formula is algebraically rearranged to isolate \( c \). You square both \( a \) and \( b \), add them together, and then calculate the square root of that sum: \( c = \sqrt{a^2 + b^2} \).

Solving for a Missing Leg (\( a \) or \( b \))

If you are given the hypotenuse (\( c \)) and one leg (for example, \( b \)), you must manipulate the formula using subtraction. Square the hypotenuse, subtract the square of the known leg, and then take the square root of the result to find the missing leg: \( a = \sqrt{c^2 - b^2} \). It is critical to remember that the hypotenuse (\( c \)) must always be a larger number than either leg; otherwise, the triangle cannot physically exist.

Frequently Asked Questions

Does the Pythagorean theorem work for all triangles? +

No. The standard Pythagorean theorem (\( a^2 + b^2 = c^2 \)) strictly applies only to right-angled triangles (triangles containing one perfect 90-degree angle). For non-right triangles, you must use the Law of Cosines.

What is a Pythagorean triple? +

A Pythagorean triple consists of three positive whole numbers that perfectly satisfy the theorem. The most famous and common example is the 3-4-5 triangle, where \( 3^2 + 4^2 = 5^2 \) (9 + 16 = 25).

Why must 'c' be the largest number? +

In geometry, the longest side of any triangle must always be situated opposite the largest angle. Since a right triangle contains a 90-degree angle (the largest possible angle in that triangle), the side opposite to it—the hypotenuse (\( c \))—must be the longest side.