Sides of the base of a regular quadrangular pyramid 15√2, height 21. Find the side edge of the pyramid and its surface area?

At the base is a square, therefore we can find its diagonal by the Pythagorean theorem = √900 = 30
Find the side in the same way, by the Pythagorean theorem:
It is equal to = √ (21 * 21 + 15 * 15) = √ (666) = 3 √74

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