A frustum is formed when a plane parallel to a cone's base cuts off the upper portion as shown. A cone is shown. The top of the cone is cut off to form a frustum of the bottom portion. The cone has a radius of 3.5 and a height of 8. The frustum has a height of 11 and a radius of 7.5. Which expression represents the volume, in cubic units, of the frustum? One-thirdπ(7.52)(11) – One-thirdπ(3.52)(8) One-thirdπ(7.52)(11) + One-thirdπ(3.52)(8) One-thirdπ(7.52)(19) – One-thirdπ(3.52)(8) One-thirdπ(7.52)(19) + One-thirdπ(3.52)(8)

(b) 240

step-by-step explanation:

first, we use the pythagorean formula using the given side lengths to find x. then we use x to find the side lengths. then we add the side lengths to find the perimeter.

pythagorean theorem formula:

a^2 + b^2 = c^2

(x - 20)^2 + (x - 40)^2 = x^2

x^2 - 40x + 400 + x^2 - 80x + 1600 = x^2

x^2 -120x + 2000 = 0

(x - 100)(x - 20) = 0

x - 100 = 0 or x - 20 = 0

x = 100 or x = 20

we see that the solution x = 20 must be discarded because it will give a negative side length and a side length of 0. the only valid solution is x = 100.

perimeter = sum of the lengths of the sides

perimeter = x + x - 20 + x - 40

perimeter = 3x - 60

replace x with 100.

perimeter = 3(100) - 60

perimeter = 300 - 60

perimeter = 240