Question 24 of 35advanced🔍 AnalyzeLong Answer5 marks

The relation ff is defined by f(x)={x2,0≤x≤33x,3≤x≤10f(x) = \begin{cases} x^2, 0 \leq x \leq 3 \\ 3x, 3 \leq x \leq 10 \end{cases}

The relation gg is defined by g(x)={x2,0≤x≤23x,2≤x≤10g(x) = \begin{cases} x^2, 0 \leq x \leq 2 \\ 3x, 2 \leq x \leq 10 \end{cases}

Show that ff is a function and gg is not a function.

Correct Answer

To determine whether the given relations are functions, we need to check if each element in the domain has exactly one image.

For relation f:

The relation f is defined by f(x)={x2,0≤x≤33x,3≤x≤10f(x) = \begin{cases} x^2, & 0 \leq x \leq 3 \\ 3x, & 3 \leq x \leq 10 \end{cases}

The domain of f is [0,10][0, 10]. We need to verify that at the point where both definitions overlap (x=3x = 3), the values are equal.

At x=3x = 3:

  • From first definition: f(3)=32=9f(3) = 3^2 = 9
  • From second definition: f(3)=3(3)=9f(3) = 3(3) = 9

Since both definitions give the same value at x=3x = 3, every element in the domain [0,10][0, 10] has exactly one image. Therefore, f is a function.

For relation g:

The relation g is defined by g(x)={x2,0≤x≤23x,2≤x≤10g(x) = \begin{cases} x^2, & 0 \leq x \leq 2 \\ 3x, & 2 \leq x \leq 10 \end{cases}

The domain of g is [0,10][0, 10]. We need to check the point where both definitions overlap (x=2x = 2).

At x=2x = 2:

  • From first definition: g(2)=22=4g(2) = 2^2 = 4
  • From second definition: g(2)=3(2)=6g(2) = 3(2) = 6

Since both definitions give different values at x=2x = 2, the element 2 has two images (4 and 6). This violates the definition of a function. Therefore, g is not a function.

Exercise: Miscellaneous Exercise on Chapter 2 | Q: 1 | (Page 17)
For More Understanding

Explanation

The question tests understanding of the definition of a function. A relation is a function if and only if each element in the domain has exactly one unique image. For piecewise-defined relations, we must check the boundary points where two definitions overlap. If both definitions give the same value at the boundary, the relation is a function. If they give different values, the relation is not a function because one element would have two images.

Solution Steps

  1. Step 1: Identify the domain of f as [0,10][0, 10] and check the overlap point x=3x = 3

  2. Step 2: Calculate f(3)f(3) from both definitions: both give 99, so f is a function

  3. Step 3: Identify the domain of g as [0,10][0, 10] and check the overlap point x=2x = 2

  4. Step 4: Calculate g(2)g(2) from both definitions: one gives 44, the other gives 66

  5. Step 5: Conclude that g is not a function since x=2x = 2 has two different images