An octagonal based pyramid has base side lengths of 20 cm and slant height of 80 cm. What is the surface area?

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  800(9 +√2) cm² ≈ 8331.4 cm²

Step-by-step explanation:

The surface area of the pyramid is the sum of the areas of the base and triangular faces.

The base area is given by ...

  A = 2(1 +√2)s² . . . . . where s is the length of one side

  A = 2(1 +√2)(20 cm)² = 800(1 +√2) cm²

The lateral area is given by ...

  A = (1/2)Ph . . . . . where P is the perimeter of the base and h is the slant height

  A = (1/2)(8)(20 cm)(80 cm) = 6400 cm²

Then the total surface area of the pyramid is ...

  SA = (800(1 +√2) +6400) cm² = 800(9 +√2) cm² ≈ 8331.4 cm²

angle addition postulate

2x=56

step-by-step explanation:

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