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!

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

What is the domain of the above equation?

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

Exercise #1

Look at the following function:

2x+29x+6 \frac{2x+2}{9x+6}

What is the domain of the function?

Video Solution

Step-by-Step Solution

To solve this problem, we will determine the domain of the rational function by following these steps:

  • Step 1: Identify the denominator of the function, which is 9x+6 9x + 6 .
  • Step 2: Set the denominator equal to zero to find values of x x that need to be excluded from the domain: 9x+6=0 9x + 6 = 0 .
  • Step 3: Solve the equation 9x+6=0 9x + 6 = 0 for x x .
  • Step 4: To solve, subtract 6 from both sides to get 9x=โˆ’6 9x = -6 .
  • Step 5: Divide each side by 9 to solve for x x , resulting in x=โˆ’23 x = -\frac{2}{3} .
  • Step 6: The domain of the function excludes the value x=โˆ’23 x = -\frac{2}{3} since it makes the denominator zero.

Thus, the domain of the given function is all real numbers except x=โˆ’23 x = -\frac{2}{3} , expressed as xโ‰ โˆ’23 x \ne -\frac{2}{3} .

Therefore, the correct choice for the domain is: xโ‰ โˆ’23 x\ne-\frac{2}{3} .

Answer

xโ‰ โˆ’23 x\ne-\frac{2}{3}

Exercise #2

Given the following function:

5โˆ’x2โˆ’x \frac{5-x}{2-x}

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

Video Solution

Step-by-Step Solution

To determine the domain of the function 5โˆ’x2โˆ’x \frac{5-x}{2-x} , we need to identify and exclude any values of x x that make the function undefined. This occurs when the denominator equals zero.

  • Step 1: Set the denominator equal to zero:
    2โˆ’x=0 2-x = 0
  • Step 2: Solve for x x :
    Adding x x to both sides gives 2=x 2 = x . Hence, x=2 x = 2 .

This means that the function is undefined when x=2 x = 2 . Therefore, the domain of the function consists of all real numbers except x=2 x = 2 .

Thus, the domain is: xโ‰ 2 x \ne 2 .

The correct answer choice is:

Yes, xโ‰ 2 x\ne2

Answer

Yes, xโ‰ 2 x\ne2

Exercise #3

Given the following function:

2421xโˆ’7 \frac{24}{21x-7}

What is the domain of the function?

Video Solution

Step-by-Step Solution

To determine the domain of the function 2421xโˆ’7 \frac{24}{21x-7} , we need to ensure that the denominator is not equal to zero.

Step 1: Set the denominator equal to zero and solve for x x :

  • 21xโˆ’7=0 21x - 7 = 0

  • 21x=7 21x = 7

  • x=721 x = \frac{7}{21}

  • x=13 x = \frac{1}{3}

The function is undefined when x=13 x = \frac{1}{3} because it would cause division by zero.

Step 2: The domain of the function is all real numbers except x=13 x = \frac{1}{3} .

Therefore, the domain of the function is all x x such that xโ‰ 13 x \neq \frac{1}{3} .

Thus, the correct answer is xโ‰ 13 \boxed{ x\ne\frac{1}{3}} .

Answer

xโ‰ 13 x\ne\frac{1}{3}

Exercise #4

22(2xโˆ’1)=30 22(\frac{2}{x}-1)=30

What is the domain of the equation above?

Video Solution

Step-by-Step Solution

To find the domain of the given function 22(2xโˆ’1)=30 22\left(\frac{2}{x} - 1\right) = 30 , follow these steps:

  • Identify critical terms: The term 2x\frac{2}{x} is undefined when x=0 x = 0 because division by zero is undefined.
  • We need to exclude x=0 x = 0 from the domain to ensure the function remains defined.
  • The correct domain for the equation is all real numbers except x=0 x = 0 .

Thus, the domain of the equation is xโ‰ 0 x \neq 0 .

Therefore, the solution to the problem is xโ‰ 0 x \neq 0 .

Answer

xโ‰ 0

Exercise #5

2xโˆ’3=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 2xโˆ’3=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.

xamp;=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 xโ‰ 0 x \neq 0 .

The correct solution to the problem is: x โ‰  0.

Answer

xโ‰ 0

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