# 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.