# 4.8 Properties of Two-dimensional Shapes

## Unit Goals

- Students classify triangles and quadrilaterals based on the properties of their side lengths and angles, and learn about lines of symmetry in two-dimensional figures. They use their understanding of these attributes to solve problems, including problems involving perimeter and area.

### Section A Goals

- Classify triangles (including right triangles), parallelograms, rectangles, rhombuses, and squares based on the properties of their side lengths and angles.
- Identify and draw lines of symmetry in two-dimensional figures.

### Section B Goals

- Solve problems involving unknown side lengths, perimeter, area, and angle measurements using the known attributes and properties of two-dimensional shapes.

### Glossary Entries

**acute angle**An angle that measures less than 90 degrees.**angle**A figure made up of two rays that share the same endpoint.**common denominator**The same denominator in two or more fractions. For instance, \(\frac{1}{4}\) and \(\frac{5}{4}\) have a common denominator.**composite number**A whole number with more than 1 factor pair.**denominator**The bottom part of a fraction that tells how many equal parts the whole was partitioned into.**dividend**The number being divided. For example, when 37 is divided by 5, we call 37 the dividend.**equivalent fractions**Fractions that have the same size and describe the same point on the number line. For example, \(\frac{1}{2}\) and \(\frac{2}{4}\) are equivalent fractions.**factor pair of a whole number**A pair of whole numbers that multiply to result in that number. For example, 5 and 4 are a factor pair of 20.**intersecting lines**Lines that cross.**line**A set of points that are arranged in a straight way and extend infinitely in opposite directions.

**line of symmetry**A line that divides a figure into two halves that match up exactly when the figure is folded along the line.**mixed number**A number expressed as a whole number and a fraction less than 1.**multiple of a number**The result of multiplying that number by a whole number. For example, 18 is a multiple of 3, because it is a result of multiplying 3 by 6.**numerator**The top part of a fraction that tells how many of the equal parts are being described.

**obtuse angle**An angle that measures greater than 90 degrees.**parallel lines**Lines that never intersect.**perpendicular lines**Lines that intersect creating right angles.**point**A location along a line or in space.

**prime number**A whole number that is greater than 1 and has exactly one factor pair: the number itself and 1.**ray**A line that ends at one point and goes on in the other direction.**remainder**The number left over when we take away as many equal groups as we can from a number.**right angle**An angle with a measurement of 90 degrees.**right triangle**A triangle with a 90 degree angle.**rounding**A formal way to say which number a given number is closer to. For example, for 182, the number 180 is the closest multiple of ten and 200 is the closest multiple of a hundred. We can round 182 to 180 (if rounding to the nearest ten) or 200 (if rounding to the nearest hundred).

**segment or line segment**A part of a line with two endpoints.

**straight angle**An angle that measures 180 degrees.**symmetry**A figure has symmetry if its parts can match up exactly when the figure is folded or rotated.**vertex**The point where the two rays meet.