If the length of a lateral edge of a right square pyramid is 13 mm and a side of the base is 10mm, then the?

Question

slant height is? I came up with 120S.

I figured the area is 100 and the perimeter is 40. I plugged it all in and came up with this number.

Answer 1

The slant height is 12 mm.
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Ideas: Use 5-12-13 Pythagorean triple. The half of the base (5), the slant height (12) and the edge (13) form a right triangle.

Answer 2

The lateral edge is the hypotenuse of a right triangle with legs = slant height and 1/2 the base side.
So 13^ - 5^2 = slant height^2 = h^2
h^2 = sqrt(144) = 12mm