Inputing Values into a Function

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Inputing Values into a Function

In mathematics, we often assign numerical values to variables in equations or mathematical expressions. A function can be thought of as a machine: you input a value (called the input), the function processes it according to a specific rule, and produces a result (called the output). The input is usually represented by \(x)\, and the output by f(x)f(x) or yy.

Understanding Variables and Substitution

A variable is a placeholder for an unknown number, often called the "unknown". When we replace a variable with a specific value, we refer to this process as substitution.

  • If an equation contains only one variable, we can solve for its value by isolating it.
  • If an equation contains multiple variables, there can be multiple solutions. Each value substituted affects the remaining variables in the equation.

When we talk about inputting values into a function, we are essentially substituting the variables in a mathematical expression or equation with specific numerical values to evaluate the result.
Often "solving an equation" is actually finding the values of the variables inside it.

For example

Suppose we have three variables, two of which have known values:

X=3 X=3

Y=2 Y=2

Z=? Z=\text{?}

We are also given the equation:

X2+Y=Z X^2+Y=Z

Remember! when facing this kind of questions, you want to try and find the values of the variables.
To solve the problem, we will first substitute the known values into the equation:

32+2=Z 3^2+2=Z

Simplify and solve:

9+2=Z9+2=Z

Z=11Z=11

By substituting the known values and performing the necessary operations, we were able to isolate and calculate the value of ZZ

Answer: Z=11 Z=11

X Y Z By assigning the numerical value, the general form becomes a particular case

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Test yourself on domain of a function!

Given the following function:

\( \frac{5-x}{2-x} \)

Does the function have a domain? If so, what is it?

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Examples and exercises with solutions for assigning numerical value in a function

Exercise #1

Does the given function have a domain? If so, what is it?

9x4 \frac{9x}{4}

Video Solution

Step-by-Step Solution

Since the function's denominator equals 4, the domain of the function is all real numbers. This means that any one of the x values could be compatible.

Answer

No, the entire domain

Exercise #2

Look at the following function:

5x \frac{5}{x}

Does the function have a domain? If so, what is it?

Video Solution

Step-by-Step Solution

Since the unknown variable is in the denominator, we should remember that the denominator cannot be equal to 0.

In other words, x≠0 x\ne0

The domain of the function is all those values that, when substituted into the function, will make the function legal and defined.

The domain in this case will be all real numbers that are not equal to 0.

Answer

Yes, x≠0 x\ne0

Exercise #3

Look the following function:

15x−4 \frac{1}{5x-4}

What is the domain of the function?

Video Solution

Step-by-Step Solution

To determine the domain of the function 15x−4 \frac{1}{5x-4} , we need to find the values of x x for which the function is undefined. This occurs when the denominator equals zero:

First, set the denominator equal to zero:
5x−4=0 5x - 4 = 0

Next, solve for x x :
5x=4 5x = 4
x=45 x = \frac{4}{5}

The function is undefined at x=45 x = \frac{4}{5} . Therefore, the domain of the function includes all real numbers except x=45 x = \frac{4}{5} .

In mathematical notation, the domain is:
x≠45 x \ne \frac{4}{5} .

This matches choice 3 among the given options.

Answer

x≠45 x\ne\frac{4}{5}

Exercise #4

Look at the following function:

2010x−5 \frac{20}{10x-5}

What is the domain of the function?

Video Solution

Step-by-Step Solution

To determine the domain of the function 2010x−5 \frac{20}{10x-5} , we need to ensure that the denominator is not zero.

  • Step 1: Identify the denominator, which is 10x−5 10x - 5 .
  • Step 2: Set the denominator equal to zero and solve for x x . This gives us the equation:

10x−5=0 10x - 5 = 0

  • Step 3: Add 5 to both sides of the equation:

10x=5 10x = 5

  • Step 4: Divide both sides by 10 to isolate x x :

x=510 x = \frac{5}{10}

  • Step 5: Simplify the fraction:

x=12 x = \frac{1}{2}

This means that the function is undefined at x=12 x = \frac{1}{2} . Therefore, the domain of the function is all real numbers except x=12 x = \frac{1}{2} .

Therefore, the domain of the function is x≠12 x \ne \frac{1}{2} .

Answer

x≠12 x\ne\frac{1}{2}

Exercise #5

Given the following function:

235x−2 \frac{23}{5x-2}

Does the function have a domain? If so, what is it?

Video Solution

Step-by-Step Solution

To determine the domain of the function 235x−2 \frac{23}{5x-2} , follow these steps:

  • Step 1: Identify where the function is undefined by setting the denominator equal to zero.
    Equation: 5x−2=0 5x - 2 = 0
  • Step 2: Solve the equation for x x .

Let's perform the calculation:
Step 1: Set 5x−2=0 5x - 2 = 0 .

Step 2: Solve for x x by adding 2 to both sides:
5x=2 5x = 2

Next, divide both sides by 5:
x=25 x = \frac{2}{5}

This shows that the function is undefined at x=25 x = \frac{2}{5} , thus excluding this point from the domain of the function.

The domain of 235x−2 \frac{23}{5x-2} consists of all real numbers except x=25 x = \frac{2}{5} .

Therefore, the domain is expressed as x≠25 x \ne \frac{2}{5} .

Considering the multiple-choice options, the correct choice is:

Yes, x≠25 x\ne\frac{2}{5}

Answer

Yes, x≠25 x\ne\frac{2}{5}

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