Math Problem Statement

Consider regular pentagons with side length s, area a, and perimeter p. Suppose f, g, h, and j

are functions such that:

f(s)

represents the perimeter (in cm) of a regular pentagon whose side length is s

cm.

g(p)

represents the side length (in cm) of a regular pentagon whose perimeter is p

cm.

h(s)

represents the area (in cm2) of a regular pentagon whose side length is s

cm.

j(a)

represents the side length (in cm) of a regular pentagon whose area is a

cm2.

Use function notation (using the appropriate function names given above) to represent the area of a regular pentagon whose perimeter is 132 cm.

Use function notation (using the appropriate functions names given above) to represent the perimeter of a regular pentagon whose area is 6.08 cm2.

Which of the following make sense in context? Select all that apply.

g(f(s))

j(h(s))

f(h(s))

f(j(a))

Solution

Let's first break down the given functions:

  • f(s) represents the perimeter of a regular pentagon with side length ss cm.
  • g(p) represents the side length of a regular pentagon given the perimeter pp cm.
  • h(s) represents the area of a regular pentagon given side length ss cm.
  • j(a) represents the side length of a regular pentagon given the area aa cm².

Part 1: Use function notation for a regular pentagon whose perimeter is 132 cm.

We know that the perimeter pp of a regular pentagon is given by: p=5sp = 5s where ss is the side length.

Given the perimeter is 132 cm, we want to find the side length ss. Using the function g(p)g(p) which gives the side length given the perimeter, we can write: g(132)g(132) This represents the side length of the regular pentagon whose perimeter is 132 cm.

Next, we want the area aa of the pentagon. Using the function h(s)h(s) which gives the area of the pentagon given the side length, we can express the area as: h(g(132))h(g(132)) This represents the area of the regular pentagon whose perimeter is 132 cm.

Part 2: Use function notation for the perimeter of a regular pentagon whose area is 6.08 cm².

We are given the area a=6.08a = 6.08 cm². We want to find the side length ss of the pentagon. Using the function j(a)j(a) which gives the side length given the area, we can write: j(6.08)j(6.08) This represents the side length of the regular pentagon whose area is 6.08 cm².

Finally, we want to find the perimeter pp. Since the perimeter is related to the side length by p=5sp = 5s, we use the function f(s)f(s) to get the perimeter: f(j(6.08))f(j(6.08)) This represents the perimeter of the regular pentagon whose area is 6.08 cm².

Part 3: Determine which functions make sense in context.

We need to evaluate each of the following:

  1. g(f(s))g(f(s)): This means first finding the perimeter f(s)f(s) for a given side length ss, and then finding the side length g(p)g(p) given that perimeter. This is valid because it’s essentially calculating the side length given the perimeter, so this function makes sense.

  2. j(h(s))j(h(s)): This means first finding the area h(s)h(s) for a given side length ss, and then using that area to find the side length j(a)j(a). This also makes sense, as you are correctly reversing the process from area to side length.

  3. f(h(s))f(h(s)): This means first finding the area h(s)h(s) for a given side length ss, and then trying to find the perimeter f(s)f(s) from the area. This does not make sense because the perimeter depends on the side length, not the area, and ff requires the side length, not the area.

  4. f(j(a))f(j(a)): This means first finding the side length j(a)j(a) given the area aa, and then using that side length to find the perimeter f(s)f(s). This makes sense, as it correctly calculates the perimeter from the side length obtained from the area.

Final Answer:

The valid functions in context are:

  • g(f(s))g(f(s))
  • j(h(s))j(h(s))
  • f(j(a))f(j(a))

Would you like further clarification on any part of this? Or have more questions on similar concepts? Here are some questions to explore further:

  1. How would you calculate the perimeter given the area of a hexagon instead of a pentagon?
  2. How would you derive the formula for the area of a regular polygon with nn sides?
  3. What would happen if you used the inverse functions for different shapes, such as a square?
  4. How do you compute the interior angle of a regular polygon based on its side length?
  5. How do the functions change if the polygon is irregular?

Tip: Always ensure the input to each function makes sense in terms of the domain and context, especially when working with geometric functions!

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Math Problem Analysis

Mathematical Concepts

Functions
Geometry
Perimeter
Area of Regular Polygon
Inverse Functions

Formulas

p = 5s (perimeter formula for regular pentagon)
a = (1/4)√5(5 + 2√5) * s² (area formula for regular pentagon)

Theorems

Properties of regular polygons
Inverse relationships of functions

Suitable Grade Level

Grades 9-12