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Pythagorean Theorem Calculator

Solve right-angled triangles by entering any two sides to find the third, plus angles, area, and height.

Solve Right Triangle

Geometric Proof Visualization

a b c

Understanding the Pythagorean Theorem

The **Pythagorean theorem** is one of the most fundamental principles in geometry. Discovered by the ancient Greek mathematician Pythagoras, it states that in any right-angled triangle, the sum of the squares of the lengths of the legs (a and b) is equal to the square of the length of the hypotenuse (c), which is the side opposite the right angle.

The Core Equation

a² + b² = c²

This equation can be rearranged depending on which side length is unknown:

  • Solving for Hypotenuse c: c = √(a² + b²)
  • Solving for Leg a: a = √(c² - b²)
  • Solving for Leg b: b = √(c² - a²)

Calculating Right Triangle Details

Beyond finding side lengths, a right triangle has several distinct geometric properties that our engine computes:

  • Area: Since the legs a and b are perpendicular, they act as base and height, meaning: Area = 0.5 × a × b.
  • Perimeter: The total length of the boundary: Perimeter = a + b + c.
  • Altitude to Hypotenuse (h_c): The shortest distance from the right angle to the hypotenuse: h_c = (a × b) / c.
  • Trigonometric Angles: Calculated in degrees using inverse trigonometry functions: α = arcsin(a / c) × (180 / π) and β = arcsin(b / c) × (180 / π).

Frequently Asked Questions (FAQ)

What does the Pythagorean theorem state?

It states that for any right-angled triangle, the square of the longest side (the hypotenuse) is equal to the sum of the squares of the other two sides. This is written as a² + b² = c².

Can this formula be used on any type of triangle?

No. It only works on right-angled triangles—triangles that contain one angle of exactly 90 degrees.

What is a Pythagorean triple?

It is a set of three positive integers that fit the theorem perfectly without any decimals. Popular examples include 3, 4, 5 and 5, 12, 13.

How do you solve for a leg instead of the hypotenuse?

Subtract the square of the known leg from the square of the hypotenuse, then take the square root of that result. The formula is a = √(c² - b²) or b = √(c² - a²).

What happens if the hypotenuse is shorter than the known leg?

That is mathematically impossible for a real right triangle because the hypotenuse must always be the longest side. The calculator will show an error if you enter a leg that is longer than the hypotenuse.

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About This Calculator

Target Audience: Students, educators, engineers & everyday problem solvers

What Does This Calculator Do?

The Pythagorean Theorem Calculator helps you find the missing side of a right-angled triangle. Whether you know the lengths of the two straight sides (legs) and need the diagonal side (hypotenuse), or you need to find a missing leg, this tool solves the math instantly. It is perfect for carpentry, landscaping, and school geometry tasks.

How to Use It

  1. Enter Known Sides: Input values for at least two sides of the triangle: Side A, Side B, or the Hypotenuse (Side C).
  2. Click Calculate: The tool resolves the missing length using square root math.
  3. Read the Breakdown: View the step-by-step formula steps showing how the sides relate.

The Logic Explained Simply

  • The Concept: For any right-angled triangle (a triangle with one 90-degree corner), the square of the longest side (the hypotenuse) is always equal to the sum of the squares of the other two sides.
  • The Formula: A² + B² = C²
  • Solving for Hypotenuse (C): C = √(A² + B²)
  • Solving for Side A: A = √(C² - B²)

Real-World Calculation Breakdown

Imagine you are putting up a ladder against a wall. The wall is 12 feet high, and you place the base of the ladder 5 feet away from the wall. You need to know how long the ladder should be.

  1. The distance along the ground (Side A) is 5 feet.
  2. The height up the wall (Side B) is 12 feet.
  3. Apply the formula: 5² + 12² = 25 + 144 = 169.
  4. Find the square root of 169: √169 = 13.
  5. You need a ladder that is exactly 13 feet long to reach the top of the wall safely!

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