Lines of symmetry of an isosceles triangle

Step by step

The question

Question: how many lines of symmetry does an isosceles triangle have?

1 Try the folds

Imagine folding the shape along a line.

If the two halves match exactly, it is a line of symmetry.

Fold through a corner and the middle of the opposite side.

The halves match: line 1.

Fold across the middle.

The corners do not meet.

It is not a line of symmetry.

2 Count the lines

We found 1.

So an isosceles triangle has 1 line of symmetry.

Careful!

Only the fold down the middle works.

The other sides are not the same length.

3 Check

Let's check.

Fold along line 1: this corner lands on that corner.

Every corner lands on a corner.

Right!

Let's look back.

First: try the folds.

Then: count the lines.

Last: check.