Pythagoras theorem
In a right triangle, the square of the hypotenuse equals the sum of the squares of the other two sides.
Practice This ConceptMain explanation
Teacher explanation
This theorem works only in a right triangle. The longest side, called the hypotenuse, is opposite the right angle, and that side must be used as c in the formula.
Example
For a right triangle with legs 6 cm and 8 cm, the hypotenuse is 10 cm because 6² + 8² = 10².
Simple analogy
Right angle first, hypotenuse last.
Common confusion
Students may apply the formula to a triangle that is not right-angled, or choose the wrong side as the hypotenuse.
Exam tip
First identify the right angle and the longest side before writing the formula.
Study the pythagoras theorem diagram carefully
Use the labelled diagram to keep pythagoras theorem clear in short answers and revision.
What this diagram makes clear
This diagram keeps the labels and direction of pythagoras theorem in the right order.
Where this helps in exams
Use this for labelled diagram work and short exam answers on pythagoras theorem.
Revision cue
Revise pythagoras theorem through the labels before writing the answer.
Answer writing and exam use
1-mark use
Write the exact meaning of pythagoras theorem in one clean line.
2-mark use
Define pythagoras theorem and add one example or condition.
3-mark use
Explain pythagoras theorem, show the method or example, and mention the common mistake.
Practice this concept with focused MCQs
Open the concept quiz intro first, review the test details, and then start a focused MCQ set from this concept only. Instant score and answer review are live now.
Help improve this page
Found something confusing, incorrect, or missing?