Classifying Triangles — Answer Key
Part A: Multiple Choice
Circle the best answer for each question.
1. How many lines of symmetry does an equilateral triangle have?
A) 0
B) 1
C) 2
D) 3
Each vertex of an equilateral triangle has a line of symmetry to the midpoint of the opposite side, giving 3 lines.
2. How many lines of symmetry does an isosceles triangle have?
A) 0
B) 1
C) 2
D) 3
An isosceles triangle has exactly 1 line of symmetry running from the apex to the midpoint of the base.
3. How many lines of symmetry does a scalene triangle have?
A) 0
B) 1
C) 2
D) 3
A scalene triangle has 0 lines of symmetry because none of its sides are congruent.
4. Why does an equilateral triangle have more lines of symmetry than a scalene triangle?
A) Equilateral has three congruent sides while scalene has none
B) Scalene triangles always have right angles
C) Equilateral triangles only have one congruent side
D) Scalene triangles have three lines of symmetry
Lines of symmetry require congruent sides; equilateral has three congruent sides, scalene has zero.
Part B: Fill in the Blank
Write the correct answer on each line.
1. An equilateral triangle has 3 lines of symmetry.
Each vertex pairs with the opposite side's midpoint, giving 3 lines of symmetry.
2. An isosceles triangle has 1 line(s) of symmetry.
The single line of symmetry runs through the apex angle to the midpoint of the base.
3. A scalene triangle has 0 line(s) of symmetry.
Without any congruent sides, a scalene triangle cannot be folded onto itself, so it has 0 lines.
4. A triangle has lines of symmetry only along sides that are congruent in length.
A line of symmetry only works when the two halves match, which requires congruent sides on either side.
5. An equilateral triangle's three lines of symmetry each pass through one vertex and the midpoint of the opposite side.
Lines of symmetry in an equilateral triangle bisect each side, going from a vertex to the midpoint opposite.