Are the Sides of a Right Angled Triangle Equal?

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A right triangle is a type of triangle that contains one 90 degree angle. The side opposite the 90 degree angle is called the hypotenuse, while the other two sides are called legs. A common question that arises with right triangles is: are the sides of a right angled triangle equal?

The Hypotenuse is Always the Longest Side

The simple answer is no, the sides of a right triangle are not necessarily equal. While it is possible for a right triangle to have two equal sides (known as an isosceles right triangle), this is not always the case.

The main rule governing the sides of a right triangle is:

The hypotenuse is always the longest side.

This is because of the Pythagorean theorem, which states:

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


a^2 + b^2 = c^2


  • a and b are the lengths of the legs
  • c is the length of the hypotenuse

Since the hypotenuse is always the longest side, it is not possible for all three sides of a right triangle to be equal. The only possibility for a right triangle to have equal sides is if it is an isosceles right triangle.

Examples of Right Triangles With Unequal Sides

To demonstrate that right triangles can have unequal side lengths, here are some examples:

3-4-5 Right Triangle

One of the most commonly known right triangles is the 3-4-5 triangle. As the name suggests, this triangle has side lengths of 3, 4, and 5 units. The hypotenuse is 5 units long, while the legs measure 3 and 4 units. This triangle clearly has unequal sides, yet satisfies the Pythagorean theorem:

32 + 42 = 9 + 16 = 25 = 52

5-12-13 Right Triangle

Another well-known right triangle is the 5-12-13 triangle. Here the shortest leg is 5 units, the longer leg is 12 units, and the hypotenuse is 13 units long. Again, all three sides are clearly of different lengths:

52 + 122 = 25 + 144 = 169 = 132

These examples demonstrate that having a 90 degree angle does not necessitate the sides being equal lengths. As long as the Pythagorean theorem is satisfied, any combination of side lengths is possible.

Special Case: Isosceles Right Triangle

There is one special scenario in which a right triangle can have two equal sides. This is called an isosceles right triangle.

In an isosceles right triangle, the hypotenuse remains the longest side, but the two legs are of equal length. This creates two 45-45-90 degree angles along with the 90 degree angle.

For an isosceles right triangle with legs of length x, the hypotenuse must be x√2 based on the Pythagorean theorem:

x2 + x2 = (x√2)2 2×2 = 2×2 √2x = x√2

Some examples of isosceles right triangles:

  • Legs of 3, hypotenuse of 3√2
  • Legs of 5, hypotenuse of 5√2
  • Legs of 12, hypotenuse of 12√2

While the isosceles case allows for two equal sides on a right triangle, it is still not possible for all three sides to be equal lengths. The hypotenuse is always longer than the legs.

Why Unequal Sides Are Possible

Now that we’ve seen examples of right triangles with unequal sides, it raises the question: why is this possible? Why isn’t having a 90 degree angle enough to force the sides to be equal?

The reason comes down to how right triangles are constructed:

Step 1) Establish One 90 Degree Angle

By definition, all right triangles have one angle measuring exactly 90 degrees. This can occur anywhere within the triangle.

Step 2) Fill in the Remaining Angles

With one angle locked in at 90 degrees, the other two angles must sum to 90 degrees to complete the triangle. There are many possibilities for these two angles, as long as they total 90 degrees when added together.

For example, the angles could be 45 and 45 degrees. Or they could be 30 and 60 degrees. Or even 20 and 70 degrees.

Step 3) Construct the Sides

After the angles are established, the side lengths can be set based on these angles and proportions within the triangle.

Since the angles can have different measurements, the resulting side lengths will also typically be different. Only in the isosceles right triangle case will two sides end up equal.

So in summary, it is the flexibility in constructing the non-right angles that allows for right triangles with unequal sides. The 90 degree angle alone is not sufficient to mandate all sides being the same length.

Practical Applications of Right Triangles

While right triangles may seem abstract, they have many practical uses across different fields:

Architecture and Construction

Right triangles are essential in architecture and construction for determining measurements and angles. The 3-4-5 and 5-12-13 triangles are commonly used in this context.

Geography and Navigation

Maps employ right triangles to represent distances and directions. Triangulation using multiple right triangles is key for navigation.

Physics and Engineering

The intersections of forces often form right triangles, which allow physicists and engineers to calculate resultant forces using vector math.

Computer Graphics

3D computer animation relies on right triangles and vectors to simulate lighting, shadows, and positioning of objects on screen.

So in many STEM fields, right triangles with unequal sides play an integral role in core calculations and real-world applications. The flexibility provided by unequal sides makes right triangles a versatile geometric shape.

How to Remember That Sides Can Be Unequal

Since students often mistakenly assume the sides of a right triangle should be equal, here are some tips to remember that unequal sides are possible:

  • Visualize examples like the 3-4-5 and 5-12-13 triangles. The different side lengths should be a clear indicator.
  • Memorize that the hypotenuse is always the longest side based on the Pythagorean theorem. This rules out all sides being equal.
  • Understand that the angles other than 90 degrees can vary, leading to different side lengths. Only isosceles triangles have equal legs.
  • Try constructing right triangles of your own with unequal sides that satisfy the Pythagorean theorem. This hands-on experience can solidify the concept.
  • Think of practical examples like architecture and navigation that rely on right triangles with unequal sides for calculations.

With a bit of practice visualizing and constructing examples, the fact that right triangle sides can be unequal should become clear and intuitive. Mastering right triangles is key for excelling in geometry and other math topics.


In summary, while an isosceles right triangle can have two equal sides, a right triangle does not necessarily have all equal sides. The definitive rule is that the hypotenuse is always longest, preventing the possibility of all sides being equal lengths. It is the variability in the non-right angles that allows for the legs to be different – as long as the total is 90 degrees. Right triangles play an important role across STEM fields like architecture and physics thanks to their versatility. With some dedicated practice and memorization tricks, the fact that right triangle sides can be unequal should stick. Understanding right triangle geometry paves the way for success in math classes and beyond.

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