Question 990911
The diagonal is the hypotenuse of a right triangle.
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c = diagonal = 30 cm
{{{a^2 + b^2 = c^2}}}
Find the other side.
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Then, the perimeter = 2L + 2W where L and W are the sides.
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That's some "lawn" - about 2 inches on a side.  Is this for a doll house?