An isosceles triangle is an example of a shape with exactly one line of symmetry. The line runs vertically from the top vertex to the midpoint of the base, dividing the triangle into two congruent halves. This symmetry arises from the two equal sides and the equal angles opposite them. The line of symmetry ensures that the shape maintains balance, with each half mirroring the other. Such symmetry is commonly observed in triangular designs and patterns.

For more NCERT Solutions for Class 6 Math Chapter 9 Symmetry Extra Questions and Answer:
https://www.tiwariacademy.com/ncert-solutions/class-6/maths/

The diagonals of a rectangle cannot be considered lines of symmetry because they fail to divide the shape into congruent halves. When a rectangle is folded along a diagonal, the resulting triangles have different side lengths, preventing them from overlapping perfectly. This contrasts with squares, where diagonals are symmetry lines due to equal side lengths. Thus, a rectangle has only vertical and horizontal lines of symmetry, reflecting its less symmetrical nature compared to a square.

For more NCERT Solutions for Class 6 Math Chapter 9 Symmetry Extra Questions and Answer:
https://www.tiwariacademy.com/ncert-solutions/class-6/maths/