Geometry: Angles and Triangles Flashcards

Grade 7 · Math · Flashcards

Review angle types, angle relationships, and triangle classification rules.

Flashcards

Acute angle: Measures less than 90°
Right angle: Measures exactly 90°; marked with a square corner symbol
Obtuse angle: Measures between 90° and 180°
Straight angle: Measures exactly 180°; looks like a straight line
Complementary angles: Two angles that add up to 90°
Supplementary angles: Two angles that add up to 180°
Vertical angles: Opposite angles formed when two lines intersect; always congruent (equal)
Triangle Angle Sum Theorem: The interior angles of any triangle always add up to 180°
Equilateral triangle: All 3 sides equal; all 3 angles equal 60°
Isosceles triangle: Exactly 2 equal sides; the 2 base angles (opposite the equal sides) are equal
Scalene triangle: No sides equal; no angles equal
Right triangle: Contains one 90° angle; the other two angles must be complementary (sum to 90°)
Triangle Inequality Theorem: The sum of any two sides must be GREATER than the third side for a valid triangle
Finding a missing angle in a triangle: Add the two known angles and subtract from 180°: missing = 180° - angle1 - angle2