Math Problem Statement

Is this function linear, quadratic, or exponential? x y – 6 – 176.4 – 5 – 122.5 – 4 – 78.4 – 3 – 44.1 – 2 – 19.6

Solution

To determine if this function is linear, quadratic, or exponential, we need to analyze the relationship between the xx and yy values.

Step 1: Check for a linear relationship

A function is linear if the change in yy is constant for each unit change in xx. Let's check the differences between consecutive yy-values.

For x=6x = -6 to x=5x = -5: y(5)y(6)=122.5(176.4)=53.9y(-5) - y(-6) = -122.5 - (-176.4) = 53.9

For x=5x = -5 to x=4x = -4: y(4)y(5)=78.4(122.5)=44.1y(-4) - y(-5) = -78.4 - (-122.5) = 44.1

For x=4x = -4 to x=3x = -3: y(3)y(4)=44.1(78.4)=34.3y(-3) - y(-4) = -44.1 - (-78.4) = 34.3

For x=3x = -3 to x=2x = -2: y(2)y(3)=19.6(44.1)=24.5y(-2) - y(-3) = -19.6 - (-44.1) = 24.5

Since the differences are not constant, the function is not linear.

Step 2: Check for a quadratic relationship

A quadratic function has the form y=ax2+bx+cy = ax^2 + bx + c, and the second differences in the yy-values should be constant.

Let's check the second differences:

First differences:

  • 53.9,44.1,34.3,24.553.9, 44.1, 34.3, 24.5

Second differences:

  • 44.153.9=9.844.1 - 53.9 = -9.8
  • 34.344.1=9.834.3 - 44.1 = -9.8
  • 24.534.3=9.824.5 - 34.3 = -9.8

Since the second differences are constant (-9.8), the function is quadratic.

Step 3: Check for an exponential relationship

An exponential function has the form y=abxy = ab^x. To check for this, the ratio of consecutive yy-values should be constant.

Let's compute the ratios:

  • 122.5176.40.694\frac{-122.5}{-176.4} \approx 0.694
  • 78.4122.50.640\frac{-78.4}{-122.5} \approx 0.640
  • 44.178.40.563\frac{-44.1}{-78.4} \approx 0.563
  • 19.644.10.444\frac{-19.6}{-44.1} \approx 0.444

Since the ratios are not constant, the function is not exponential.

Conclusion:

This function is quadratic.

Would you like more details on quadratic functions or further questions on this topic?

Here are 5 related questions for deeper understanding:

  1. How can we find the equation of a quadratic function from data points?
  2. How can we verify if a function is quadratic by plotting it?
  3. What is the formula for calculating second differences?
  4. How can we tell if a quadratic function opens upwards or downwards?
  5. What are the real-life applications of quadratic functions?

Tip: To identify whether a function is quadratic, always check the second differences between the yy-values. If they are constant, the function is quadratic!

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Math Problem Analysis

Mathematical Concepts

Functions
Linear Functions
Quadratic Functions
Exponential Functions
Second Differences

Formulas

y = ax^2 + bx + c (Quadratic function)
y = ab^x (Exponential function)

Theorems

Second differences test for quadratic functions
Linear function test (constant first differences)
Exponential function test (constant ratios)

Suitable Grade Level

Grades 7-9