Geometry
What you must understand
Grade 4 geometry asks you to identify and draw points, lines, line segments, rays, and angles, and to classify angles as acute, right, or obtuse. You should recognize parallel and perpendicular lines and classify two-dimensional figures by their properties, including triangles (right, acute, obtuse) and quadrilaterals such as squares, rectangles, rhombuses, trapezoids, and parallelograms. You also need line symmetry: identifying lines of symmetry and drawing a figure symmetric about a given line.
Traps to watch
- Naming figures loosely. A square is also a rectangle and a rhombus. A figure can belong to more than one category, so choose the most specific name the question allows.
- Confusing lines and rays. A line extends forever in both directions; a ray has one endpoint; a line segment has two endpoints.
- Angle estimation. An angle wider than a right angle is obtuse, but one wider than a straight line (180 degrees) is not an angle in this grade's classification.
- Symmetry lines. A rectangle has two lines of symmetry, but a square has four. Do not assume all quadrilaterals are symmetric.
Rule of thumb
Classify a figure by checking its properties one at a time: number of sides, parallel sides, right angles, and equal side lengths. Use a right-angle corner to test whether an angle is exactly 90 degrees.
Worked example
A quadrilateral has four equal sides and four right angles. What is its most specific name? Four equal sides rule out a plain rectangle; four right angles rule out a plain rhombus. Both conditions together describe a square. Note that it is also a rhombus and a rectangle, but "square" is the most specific name.