Pythagorean Theorem and Geometry Flashcards

Grade 9 · Math · Flashcards

Essential terms for applying the Pythagorean Theorem and geometry concepts in Grade 9 Math.

Flashcards

Pythagorean Theorem: a² + b² = c²; true for all right triangles
Hypotenuse: Longest side of a right triangle; opposite the right angle
Leg: One of the two shorter sides of a right triangle
Pythagorean triple: Three positive integers satisfying a² + b² = c²; classic example: 3, 4, 5
Converse of Pythagorean Theorem: If a² + b² = c², the triangle must be a right triangle
Distance formula: d = √((x₂−x₁)² + (y₂−y₁)²)
Right angle: A 90° angle; indicated by a small square in diagrams
Acute triangle: All angles less than 90°; satisfies a² + b² > c²
Obtuse triangle: One angle greater than 90°; satisfies a² + b² < c²
Midpoint formula: M = ((x₁+x₂)/2, (y₁+y₂)/2) — finds the middle of a segment
Irrational length: A side whose length is a non-perfect-square under a root, e.g., √2 or √5
45-45-90 triangle: Right isosceles triangle; legs are equal; hypotenuse = leg × √2