Learn · Illustrative Mathematics K–5 · Grade 4 · Unit 7
Short lessons you can play with. Tell lines, rays, and segments apart, turn lines to make them parallel or perpendicular, measure and draw angles on a protractor, and find unknown angles, then check yourself.
Six short chapters follow the unit’s lessons in order. Each step shows one idea with something to tap or move, then a quick check. A wrong answer names the likely mistake and gives one more try. Progress is saved on this device.
Angles are in whole degrees, in multiples of 5 when read from a protractor. A right angle is 90°, a straight angle 180°, and a full turn 360°. The protractor’s inner scale counts from 0 on the right and its outer scale from 0 on the left, as on most classroom protractors.
Ray: part of a line with one endpoint. Segment: part of a line with two endpoints. Parallel: lines that never meet. Perpendicular: lines that meet at a right angle. Acute, right, obtuse, straight: angles less than 90°, exactly 90°, between 90° and 180°, and exactly 180°.
Guess the Figure (Lesson 16) is an optional lesson. Practice it all in Angle Arcade, the game for this unit.