Why does an isosceles triangle have only 1 line of symmetry?

An isosceles triangle has only one line of symmetry because it has two equal sides and one unequal side. The line of symmetry runs vertically from the apex (the vertex opposite the base) down to the midpoint of the base, effectively dividing the triangle into two mirror-image halves. Any other line drawn through the triangle will not produce symmetrical halves due to the unequal side. Thus, the unique properties of its sides lead to just one line of symmetry.