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Euclid theorems in a right triangle

Mathematics — first biennium · Lesson

Biennium · Common core

Euclid theorems in a right triangle

Euclid's second theorem links the altitude to the hypotenuse with the two leg projections: h²=p·q.

Key idea
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Similar example
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Prerequisites: Similarity and Pythagorean theorem

Goal: Apply both Euclid theorems by linking legs, altitude, hypotenuse and projections.

What you need to know before the exercises

In this lesson: Apply both Euclid theorems by linking legs, altitude, hypotenuse and projections.

New concept: In a right triangle, the altitude to the hypotenuse divides the hypotenuse into the two projections of the legs. Euclid's theorems connect legs, hypotenuse, projections and altitude; identify these segments before choosing a relation.

How to proceed: The second theorem uses only the two projections on the hypotenuse. The geometric result is a length, so take the positive square root.

You can already assume: Similarity and Pythagorean theorem.

Geometry view

Read the diagram

SVG
Geometry diagram for the exercise Altitude CH splits hypotenuse AB into projections AH and HB: the three lengths make both Euclid theorems visible. A B C H p=16q=9h=12c=25a=20b=15

Altitude CH splits hypotenuse AB into projections AH and HB: the three lengths make both Euclid theorems visible.

Try it now

Use the two projections as factors and take the positive altitude.

Guided

Completed exercises: 0/5 · Correct on first attempt: 0

How to reason

The second theorem uses only the two projections on the hypotenuse. The geometric result is a length, so take the positive square root.

Data / situation: In right triangle ABC, AH=16 and HB=9. Find CH.

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