Y 1 3x 5 Graph

Decoding the y = 1 + 3x - 5x² Graph: A Comprehensive Guide

Understanding graphs is fundamental to mastering algebra and numerous other mathematical concepts. This article will delve into the intricacies of graphing the quadratic equation y = 1 + 3x - 5x², exploring its key features, such as intercepts, vertex, and axis of symmetry. We will also discuss how to accurately plot this function and interpret its shape, providing a thorough understanding for students of all levels.

Introduction

The equation y = 1 + 3x - 5x² represents a quadratic function, a type of polynomial function with a degree of 2. Quadratic functions are characterized by their parabolic shape when graphed. This particular equation has a negative leading coefficient (-5), indicating that the parabola will open downwards, meaning it will have a maximum point rather than a minimum. Understanding its characteristics requires examining its intercepts, vertex, and axis of symmetry. This guide provides a step-by-step approach to graphing this function and interpreting its features.

1. Finding the y-intercept

The y-intercept is the point where the graph crosses the y-axis. This occurs when x = 0. Substituting x = 0 into the equation, we get:

y = 1 + 3(0) - 5(0)² = 1

Therefore, the y-intercept is (0, 1).

2. Finding the x-intercepts (Roots or Zeros)

The x-intercepts are the points where the graph crosses the x-axis. These occur when y = 0. To find the x-intercepts, we need to solve the quadratic equation:

0 = 1 + 3x - 5x²

This equation is not easily factorable, so we'll use the quadratic formula:

x = [-b ± √(b² - 4ac)] / 2a

Where a = -5, b = 3, and c = 1. Substituting these values, we get:

x = [-3 ± √(3² - 4(-5)(1))] / 2(-5) x = [-3 ± √(9 + 20)] / -10 x = [-3 ± √29] / -10

This gives us two x-intercepts:

x₁ = [-3 + √29] / -10 ≈ 0.317 x₂ = [-3 - √29] / -10 ≈ 0.633

Therefore, the x-intercepts are approximately (0.317, 0) and (0.633, 0).

3. Finding the Vertex

The vertex is the highest or lowest point on the parabola. For a parabola opening downwards (like ours), it represents the maximum point. The x-coordinate of the vertex can be found using the formula:

x = -b / 2a

Substituting a = -5 and b = 3, we get:

x = -3 / 2(-5) = 3/10 = 0.3

To find the y-coordinate, substitute x = 0.3 back into the original equation:

y = 1 + 3(0.3) - 5(0.3)² = 1 + 0.9 - 0.45 = 1.45

Therefore, the vertex is (0.3, 1.45).

4. Finding the Axis of Symmetry

The axis of symmetry is a vertical line that passes through the vertex, dividing the parabola into two symmetrical halves. Its equation is simply:

x = -b / 2a = 0.3

Therefore, the axis of symmetry is x = 0.3.

5. Plotting the Graph

Now that we have the y-intercept, x-intercepts, vertex, and axis of symmetry, we can plot the graph. Start by plotting these key points on a coordinate plane. Then, sketch a smooth parabola passing through these points, remembering that it opens downwards. You can also calculate additional points by substituting different x-values into the equation to improve the accuracy of your sketch. For instance, you could calculate the y-values for x = -1, x = 1, and x = 2.

6. Explanation of the Graph's Shape and Characteristics

The graph of y = 1 + 3x - 5x² is a downward-opening parabola. Its shape is determined by the negative coefficient of the x² term. The vertex represents the maximum value of the function. The axis of symmetry divides the parabola into two mirror images. The x-intercepts represent the points where the function's value is zero. The y-intercept represents the value of the function when x is zero. The steepness of the parabola is influenced by the magnitude of the coefficient of the x² term; a larger absolute value indicates a steeper parabola.

7. Mathematical Explanation: Completing the Square

Completing the square is another method to find the vertex of the parabola. This method involves rewriting the quadratic equation in vertex form: y = a(x - h)² + k, where (h, k) is the vertex.

Let's complete the square for y = 1 + 3x - 5x²:

1. Factor out the coefficient of x² from the x² and x terms: y = -5(x² - (3/5)x) + 1

2. Take half of the coefficient of x (-3/10), square it (9/100), and add and subtract it inside the parenthesis: y = -5(x² - (3/5)x + 9/100 - 9/100) + 1

3. Rewrite the expression inside the parenthesis as a perfect square: y = -5((x - 3/10)² - 9/100) + 1

4. Distribute the -5: y = -5(x - 3/10)² + 9/20 + 1

5. Simplify: y = -5(x - 3/10)² + 29/20

Now, the equation is in vertex form. The vertex is (3/10, 29/20), which is equivalent to (0.3, 1.45), confirming our previous result.

8. Applications of Quadratic Functions

Quadratic functions have numerous applications in various fields:

• Physics: Modeling projectile motion, where the path of a projectile follows a parabolic trajectory.
• Engineering: Designing parabolic antennas and reflectors, which focus signals efficiently.
• Business: Determining maximum profit or minimum cost, where the quadratic function represents the profit or cost as a function of production level.
• Computer Graphics: Creating curved shapes and animations.

9. Frequently Asked Questions (FAQ)

• Q: What if the parabola opens upwards? A: If the coefficient of x² is positive, the parabola opens upwards, and the vertex represents the minimum point.

• Q: Can a quadratic function have only one x-intercept? A: Yes, this occurs when the discriminant (b² - 4ac) is equal to zero. The parabola touches the x-axis at its vertex.

• Q: How can I check my graph's accuracy? A: You can use graphing calculators or online graphing tools to verify your plot. You can also calculate additional points to ensure the curve is smooth and accurate.

• Q: What does the discriminant tell us? A: The discriminant (b² - 4ac) determines the number and type of x-intercepts. If it's positive, there are two distinct real roots (x-intercepts). If it's zero, there is one real root (the parabola touches the x-axis at the vertex). If it's negative, there are no real roots (the parabola does not intersect the x-axis).

10. Conclusion

Graphing the quadratic function y = 1 + 3x - 5x² involves a systematic approach of finding key features like intercepts, vertex, and axis of symmetry. Understanding these elements allows for accurate plotting and interpretation of the parabola's shape and characteristics. The process involves solving quadratic equations, applying the quadratic formula, and understanding the significance of the parabola’s vertex and axis of symmetry. This comprehensive guide equips you with the necessary knowledge to graph quadratic functions and understand their broader applications in various fields. Remember to practice regularly to build your confidence and proficiency in graphing and interpreting quadratic functions. Mastering this skill will pave the way for a deeper understanding of more complex mathematical concepts.