Pythagoras Theorem • Topic 3 of 3

Application in Calculating Sides and Diagonals

What are the Practical Applications of Pythagoras Theorem?

The application of Pythagoras Theorem goes far beyond basic triangles. It is an essential tool used to find unknown paths and straight lines hidden inside other geometric shapes like rectangles, squares, rhombuses, and isosceles triangles.

A prime example is calculating a diagonal. A diagonal is a straight line that cuts across a shape from one corner vertex to the opposite corner vertex. When you draw a diagonal line through a square or rectangle, it splits the shape into two symmetrical right-angled triangles.

Let us explore where these hidden right angles appear:

  • Rectangles and Squares: The corner angles are always exactly 90 degrees. Drawing a diagonal creates a right-angled triangle where the width and length are the legs, and the diagonal line is the hypotenuse.
  • Rhombuses: The two intersecting internal diagonals cross each other at a perfect 90-degree right angle. This splits a rhombus into four small internal right-angled triangles.
  • Isosceles Triangles: Drawing an altitude height line from the top vertex straight down to the base bisects it at a 90-degree angle, creating two matching right triangles.
Geometric Shape ProfileHidden Leg ElementsHypotenuse Element
SquareSide (s) and Side (s)Corner-to-corner Diagonal (D)
Isosceles TriangleAltitude Height (h) and Half-Base (b/2)Equal Outer Sloped Side (s)
Applications of Pythagoras TheoremFinding the diagonal of a rectanglel=8, b=6 → d = √(8²+6²) = √100 = 10Height of a ladder problemLadder 13m, base 5m from wall → height = √(169-25) = 12mDistance between two pointsd = √[(x₂-x₁)²+(y₂-y₁)²] ← Pythagoras in disguiseIsoceles right triangleIf legs = a, hypotenuse = a√2 (45-45-90 triangle)30-60-90 triangle: sides in ratio 1 : √3 : 245-45-90 triangle: sides in ratio 1 : 1 : √2
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Worked Example

Solve a standard problem on Application in Calculating Sides and Diagonals.

Solution

Apply the formula/method shown in the concept section above.

Key Points

  • Understand the definition and properties of Application in Calculating Sides and Diagonals.
  • Study the worked examples and practice similar problems.
  • Always verify your answer using the original conditions.
Tap an option to check your answer0 / 4
Q1.The diagonal of a rectangle $l\times b$ is:
Explanation: Pythagoras.
Q2.The diagonal of a square of side $a$ is:
Explanation: $a\sqrt2$.
Q3.The diagonal of a $3\times4$ rectangle is:
Explanation: $\sqrt{9+16}=5$.
Q4.A ladder, wall and ground form a:
Explanation: Right triangle.