# Concept derivation guides

299 concept teaching guides, separate from the 36,000 individual question derivations.

[Search all questions & derivations →](/en/explore/)

1 1 results · Page 1 of 1



Concept guide



## [Right triangle: deciding in coordinates which interior angle is right](/en/derivations/derivation-mko-right-triangle-01/?from=%2Fen%2Fderivations%2F%3Fq%3Dmko-right-triangle)

In the coordinate-plane model ℝ², let A=(1,1), B=(5,3), C=(0,3). Prove that A, B, C form a nondegenerate triangle whose interior angle at A equals 90° (that is, π/2), so ABC is a right triangle; show that the other two angles are not right and that any nondegenerate triangle has at most one right angle, and identify the hypotenuse and the legs. Then, with D=(1,4), show that triangle ABD is not a right triangle.

Right triangle

derivation-mko-right-triangle-01





1 1 results · Page 1 of 1