Inputing Values into a Function

🏆Practice domain of a function

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

Start practice

Test yourself on domain of a function!

\( 2x+\frac{6}{x}=18 \)

What is the domain of the above equation?

Practice more now

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

Exercise #1

2x+6x=18 2x+\frac{6}{x}=18

What is the domain of the above equation?

Video Solution

Step-by-Step Solution

To solve this problem and find the domain for the expression 2x+6x2x + \frac{6}{x}, we apply the following steps:

  • Step 1: Identify when the fraction 6x\frac{6}{x} is undefined. This occurs when the denominator xx equals zero.
  • Step 2: To find the restriction, set the denominator equal to zero: x=0x = 0.
  • Step 3: Solve for xx to find the values excluded from the domain. Here, x0x \neq 0.

Since 6x\frac{6}{x} is undefined for x=0x = 0, the value x=0x = 0 must be excluded from the domain.
Hence, the domain of the equation is all real numbers except zero.

Therefore, the solution to the problem, indicating the domain of the expression, is x0 x \neq 0 .

Answer

x≠0

Exercise #2

2x3=4x 2x-3=\frac{4}{x}

What is the domain of the exercise?

Video Solution

Step-by-Step Solution

To solve this problem, we'll follow these steps:

  • Step 1: Identify the fraction's denominator.

  • Step 2: Determine where this denominator equals zero.

  • Step 3: Exclude this value from the domain.

Now, let's work through each step:

Step 1: The given equation is 2x3=4x 2x - 3 = \frac{4}{x} . Notice that the fraction 4x\frac{4}{x} has a denominator of xx.

Step 2: Set the denominator equal to zero to determine where it is undefined.

x=0 \begin{aligned} x &= 0 \end{aligned}

Step 3: Since the expression is undefined at x=0x = 0, we must exclude this value from the domain.

Therefore, the domain of the expression is all real numbers except 0, formally stated as x0 x \neq 0 .

The correct solution to the problem is: x ≠ 0.

Answer

x≠0

Exercise #3

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, x0 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, x0 x\ne0

Exercise #4

Look at the following function:

2x+202x10 \frac{2x+20}{\sqrt{2x-10}}

What is the domain of the function?

Video Solution

Step-by-Step Solution

To determine the domain of the function 2x+202x10 \frac{2x+20}{\sqrt{2x-10}} , we must ensure that the expression under the square root is non-negative, because the square root of a negative number is not defined in the real numbers.

We start by analyzing the denominator, specifically the square root, 2x10\sqrt{2x-10}. For the square root to be valid (for real numbers), we require:

  • 2x100 2x-10 \geq 0

Now, solve the inequality 2x1002x - 10 \geq 0:

  • Add 10 to both sides: 2x102x \geq 10
  • Divide both sides by 2: x5x \geq 5

However, since the expression 2x102x-10 also prohibits zero in the denominator (as the square root in the denominator cannot be zero), we strictly have:

  • x>5x > 5

Thus, the domain of the function is all xx such that x>5x > 5.

Therefore, the domain of the function 2x+202x10\frac{2x+20}{\sqrt{2x-10}} is x>5 x > 5 .

Answer

x>5 x > 5

Exercise #5

What is the domain of the exercise?

5x+82x6=30 \frac{5x+8}{2x-6}=30

Video Solution

Step-by-Step Solution

To find the domain of the expression 5x+82x6=30\frac{5x+8}{2x-6} = 30, we need to identify values of xx that make the denominator of the fraction zero.

Step 1: Identify the denominator of the fraction, which is 2x62x - 6.

Step 2: Set the denominator equal to zero to find the values to exclude:

  • Solve the equation 2x6=02x - 6 = 0.
  • Add 6 to both sides: 2x=62x = 6.
  • Divide both sides by 2: x=3x = 3.

Therefore, x=3x = 3 is the value that makes the denominator zero, so it must be excluded from the domain.

Given the choices, the correct answer is x3x \neq 3.

Therefore, the domain of the expression is all real numbers except x=3x = 3.

This implies that the correct choice is:

x3 x \neq 3

Answer

x≠3

Join Over 30,000 Students Excelling in Math!
Endless Practice, Expert Guidance - Elevate Your Math Skills Today
Test your knowledge
Start practice