Answer:
569 square units
Explanation:
You want the surface area of the 8-sided shape that has a square "base" 7 units on a side, and a "height" of 20 units.
Slant height
The slant height of each triangular face is the hypotenuse of a right triangle with legs 7/2 units and 20 units. That height is ...
h = √(3.5² +20²) = √412.25 ≈ 20.304 units
Surface area
The area of one triangular face is ...
A = 1/2bh
A = 1/2(7)(20.304) . . . one face
There area 8 congruent triangular faces, so the total area is ...
A = 8(1/2)(7)(20.304) = 8(7)√412.25 ≈ 568.51 ≈ 569
The total surface area is about 569 square units.
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