The perimeter of a square is 24 cm. what is the length of the diagonal

A square is equal on all 4 sides and in this problem all sides are equal to 6. Therefore you have an isosceles right triangle with two sides of six making the Hypotenuse 6*the square root of two.
( the rule for an isosceles right triangle is the two legs are equal to X and the Hypotenuse is equal to X* the square root of 2  

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