Lines and Symmetry — Answer Key
Part A: Multiple Choice
Circle the best answer for each question.
1. Which capital letter has exactly 2 lines of symmetry?
A) A
B) H
C) T
D) E
The letter H can be folded vertically down its center and horizontally through its middle bar, and both halves match each time, giving it exactly 2 lines of symmetry.
2. How many pairs of parallel sides does a regular hexagon have?
A) 1
B) 2
C) 3
D) 6
A regular hexagon has 6 sides, and each side runs parallel to the side directly across from it. That gives 3 pairs of parallel sides in total.
3. A shape has exactly 5 lines of symmetry. What shape could it be?
A) Rectangle
B) Regular pentagon
C) Hexagon
D) Rhombus
A regular pentagon has 5 equal sides, and every regular polygon has as many lines of symmetry as it has sides. So a regular pentagon is the shape with exactly 5 lines of symmetry.
4. Two lines intersect and form four angles. If one angle is 50°, what is the angle directly across from it?
A) 40°
B) 50°
C) 130°
D) 180°
When two lines intersect, the angles directly across from each other are called vertical angles and are always equal. Since one angle is 50 degrees, the angle across from it must also be 50 degrees.
Part B: Fill in the Blank
Write the correct answer on each line.
1. When two lines intersect, the opposite angles formed are called vertical angles.
The opposite angles created when two lines cross are called vertical angles. They always have the same measure because each pair shares the same opening between the lines.
2. A regular polygon with 12 sides has 12 lines of symmetry.
A regular polygon always has the same number of lines of symmetry as it has sides. Since a 12-sided regular polygon has 12 equal sides, it has 12 lines of symmetry.
3. The diagonal of a rectangle divides it into two congruent triangles.
Drawing a diagonal across a rectangle splits it into two triangles that are exactly the same shape and size (congruent), because opposite sides of a rectangle are equal.
4. An equilateral triangle has all three sides equal in length.
The prefix "equi-" means equal and "lateral" means side, so an equilateral triangle by definition has all three sides the same length.
5. A straight angle measures 180 degrees and looks like a straight line.
A straight angle opens all the way until its two rays point in opposite directions, forming a straight line. That full half-turn measures exactly 180 degrees.