The Sum Of A Number And Its Square Is 42

Solving the Equation: The Sum of a Number and its Square is 42

Finding a number where the sum of itself and its square equals 42 might seem like a simple math problem, but it opens doors to understanding quadratic equations, their solutions, and the elegance of algebraic manipulation. This article will delve into solving this seemingly straightforward equation, exploring different methods, discussing the underlying mathematical principles, and providing a deeper understanding of quadratic equations. This exploration will also touch upon the significance of such problems in various fields of mathematics and beyond.

Introduction: Understanding the Problem

The core problem is expressed as: x + x² = 42, where 'x' represents the unknown number. This equation is a quadratic equation, meaning it involves a variable raised to the power of two. Solving this requires us to rearrange the equation into a standard quadratic form and then apply appropriate solution techniques. Understanding quadratic equations is fundamental in various areas, including physics, engineering, economics, and computer science, where they model diverse phenomena like projectile motion, curve fitting, and optimization problems.

Method 1: Rearranging and Factoring the Quadratic Equation

The first step to solving x + x² = 42 is to rearrange it into the standard quadratic form: ax² + bx + c = 0. Subtracting 42 from both sides gives us:

x² + x - 42 = 0

Now we need to factor this quadratic expression. Factoring involves finding two numbers that add up to the coefficient of 'x' (which is 1) and multiply to the constant term (-42). These numbers are 7 and -6. Therefore, the factored form of the equation is:

(x + 7)(x - 6) = 0

This equation is satisfied if either (x + 7) = 0 or (x - 6) = 0. This gives us two possible solutions:

• x = -7
• x = 6

Let's verify these solutions:

• For x = -7: (-7) + (-7)² = -7 + 49 = 42 (Correct)
• For x = 6: 6 + 6² = 6 + 36 = 42 (Correct)

Therefore, both -7 and 6 are valid solutions to the equation x + x² = 42.

Method 2: Using the Quadratic Formula

The quadratic formula provides a general solution for any quadratic equation of the form ax² + bx + c = 0. The formula is:

x = [-b ± √(b² - 4ac)] / 2a

In our equation, x² + x - 42 = 0, we have a = 1, b = 1, and c = -42. Substituting these values into the quadratic formula gives:

x = [-1 ± √(1² - 4 * 1 * -42)] / (2 * 1) x = [-1 ± √(1 + 168)] / 2 x = [-1 ± √169] / 2 x = [-1 ± 13] / 2

This leads to two solutions:

• x = (-1 + 13) / 2 = 12 / 2 = 6
• x = (-1 - 13) / 2 = -14 / 2 = -7

Again, we arrive at the same solutions: x = 6 and x = -7.

Method 3: Completing the Square

Completing the square is another technique for solving quadratic equations. The goal is to manipulate the equation into a perfect square trinomial, which can then be easily solved. Starting with x² + x - 42 = 0:

1. Move the constant term to the right side: x² + x = 42
2. Take half of the coefficient of x (which is 1), square it (1/4), and add it to both sides: x² + x + 1/4 = 42 + 1/4
3. The left side is now a perfect square trinomial: (x + 1/2)² = 169/4
4. Take the square root of both sides: x + 1/2 = ±√(169/4) = ±13/2
5. Solve for x:
   • x = -1/2 + 13/2 = 12/2 = 6
   • x = -1/2 - 13/2 = -14/2 = -7

Once again, the solutions are x = 6 and x = -7.

A Deeper Dive into Quadratic Equations

The equation x + x² = 42 exemplifies the fundamental nature of quadratic equations. These equations, characterized by their highest power of 2, are ubiquitous in various mathematical and real-world applications. The solutions to a quadratic equation represent the x-intercepts (points where the graph intersects the x-axis) of the corresponding parabola. The discriminant (b² - 4ac) within the quadratic formula determines the nature of the roots:

• b² - 4ac > 0: Two distinct real roots (as in our example).
• b² - 4ac = 0: One real root (a repeated root).
• b² - 4ac < 0: Two complex roots (involving imaginary numbers).

Applications of Quadratic Equations

The versatility of quadratic equations extends far beyond simple mathematical exercises. Here are some examples of their applications:

• Physics: Calculating projectile motion, determining the trajectory of a ball or rocket.
• Engineering: Designing curves and shapes for bridges, roads, and other structures.
• Economics: Modeling supply and demand curves, analyzing market equilibrium.
• Computer Graphics: Creating curved lines and shapes in computer-generated images.
• Finance: Calculating compound interest, analyzing investment growth.

Frequently Asked Questions (FAQ)

• Q: Can a quadratic equation have more than two solutions? A: No, a quadratic equation can have at most two solutions. This is a direct consequence of the fundamental theorem of algebra.
• Q: What if the quadratic equation cannot be factored easily? A: The quadratic formula always provides a solution, regardless of whether the equation is easily factorable.
• Q: What are complex roots? A: Complex roots involve the imaginary unit i (√-1), arising when the discriminant (b² - 4ac) is negative. These roots represent points in the complex plane, not on the real number line.
• Q: Why are there two solutions in this particular problem? A: The parabola represented by the equation x² + x - 42 = 0 intersects the x-axis at two points, corresponding to the two solutions, x = 6 and x = -7. Each solution represents a value of x that satisfies the original equation.

Conclusion: More Than Just Numbers

Solving the equation x + x² = 42 may appear as a basic algebraic exercise, but it acts as a gateway to understanding the wider world of quadratic equations and their profound significance. The multiple methods presented – factoring, the quadratic formula, and completing the square – showcase the interconnectedness of mathematical concepts. By mastering these techniques and comprehending the underlying principles, we gain a powerful tool applicable across numerous scientific and practical disciplines. The seemingly simple problem highlights the beauty and utility of mathematics, revealing the hidden elegance within seemingly straightforward equations. The journey from a simple problem statement to the understanding of broader mathematical principles is a testament to the enriching power of mathematical exploration.