Pythagorean Theorem Calculator

Find the missing side of a right triangle, or check whether three sides form one. Exact answers in simplified-radical form (√50 → 5√2), with every step shown.
Computed
Solved exactly, with the simplified-radical form.
Resultexact

Hypotenuse c

5

numeric ≈ 5

Graph
a = 3b = 4c = 5123-112345 0

Step-by-step solution

  1. 1

    The Pythagorean theorem

    In a right triangle, the square of the hypotenuse equals the sum of the squares of the two legs.

    a2+b2=c2a^2 + b^2 = c^2
  2. 2

    Substitute the known sides

    Substitute the legs a = 3 and b = 4 into the theorem.

    32+42=c23^2 + 4^2 = c^2
  3. 3

    Compute exactly

    Square each leg and add: 9 + 16 = 25. Fraction arithmetic keeps this exact.

    32+42=253^2 + 4^2 = 25
  4. 4

    Take the square root

    Take the square root of both sides: c = √25.

    c=25c = \sqrt{25}
  5. 5

    Simplify the radical

    The value under the root, 25, is a perfect square, so the answer is exactly 5, with no radical left.

    c=25=5c = \sqrt{25} = 5
  6. 6

    Result

    With legs a = 3 and b = 4, the hypotenuse is c = 5 ≈ 5.

    c=5≈5c = 5 \approx 5

About the Pythagorean theorem

In any right triangle, the square on the hypotenuse equals the sum of the squares on the two legs: a² + b² = c². It is the foundation of distance measurement in geometry.

The converse classifies any triangle: if the sum of the two shorter squares equals the longest square it is right-angled, if the sum is greater it is acute, and if it falls short it is obtuse.

Whole-number solutions like 3-4-5 or 5-12-13 are Pythagorean triples; when the answer is not whole, this calculator keeps it exact as a simplified radical (√50 = 5√2) instead of a rounded decimal.