The cone has infinitely many planes of symmetry through its axis.
The Square Pyramid has 4 planes of symmetry, each one intersecting the apex and one of the 4 lines of symmetry of the square base.
The (isosceles) Triangular Prism has a plane of symmetry through the altitudes of each triangular face, and another bisecting and perpendicular to the long edges. (2 planes total)
The Square Prism has 4 planes of symmetry through the lines of symmetry of each square end (each of those planes contains the corresponding lines in both faces, so is perpendicular to the square end). It has a 5th plane of symmetry that bisects all of the long edges of the prism (and is parallel to the square ends). (5 planes total)
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Mathematics, published 11.05.2023
Mathematics, published 23.03.2023