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Irregular
An equilateral triangle is a regular shape because it has 3 equal sides.
No because an equilateral triangle is a regular polygon whereas an obtuse triangle is irregular
No because only an equilateral triangle is a regular polygon because it has 3 equal sides and 3 equal angles.
Each body has its own centre of gravity. The centre of gravity of two regular shapes - an equilateral triangle and a square will be different so why should the cog of a regular and an irregular shape not be different?