Problem 43 - Algebra 2

Question

Solve each equation. $$ 4 x^{2}+64=0 $$

Step-by-Step Solution

Answer

The solutions are \(x = 4i\) and \(x = -4i\).

Step 1: Isolate the Quadratic Term

Start with the equation:\[ 4x^2 + 64 = 0 \]Subtract 64 from both sides to isolate the quadratic term:\[ 4x^2 = -64 \]

Step 2: Simplify the Equation

Divide both sides of the equation by 4 to simplify:\[ x^2 = -16 \]

Step 3: Solve for x by Taking the Square Root

Take the square root of both sides to solve for \(x\). Remember that taking the square root of a negative number results in an imaginary number:\[ x = \pm \sqrt{-16} \]

Step 4: Simplify the Imaginary Number

Simplify the square root of the negative number using the imaginary unit \(i\), where \(i^2 = -1\):\[ x = \pm 4i \]

Key Concepts

Quadratic Equations

Quadratic equations are mathematical expressions that set a polynomial of degree two equal to zero. They are often written in the general form \(ax^2 + bx + c = 0\). Here, \(a\), \(b\), and \(c\) are constants, with \(a eq 0\). The simplest form of a quadratic equation is when \(b\) and \(c\) are zero, reducing it to \(ax^2 = 0\), although in practice you'll usually see all three terms present.

To solve a quadratic equation, you have several methods at your disposal. Some common techniques include:

• Factoring the quadratic expression into two binomials and using the zero product property.
• Completing the square to transform the quadratic into a perfect square trinomial.
• Using the quadratic formula, \(x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}\), which provides the solutions directly.

Quadratic equations can have two real solutions, one real solution (a repeated root), or two complex solutions when the discriminant \(b^2 - 4ac\) is negative. This is where imaginary numbers and understanding square roots of negative numbers become crucial.

Imaginary Numbers

Imaginary numbers arise when we take the square root of negative numbers, which does not result in a real number. Instead, mathematicians introduced the concept of imaginary numbers where \(i\) is defined such that \(i^2 = -1\).

When we solve quadratic equations with a negative discriminant, such as \(x^2 = -16\), the solutions are not real numbers but involve \(i\). For example, \(\sqrt{-16} = 4i\).

• The imaginary unit \(i\) represents a rotational operation by 90 degrees in the complex plane.
• Imaginary numbers can be added, multiplied, and manipulated in conjunction with real numbers to form complex numbers, such as \(a + bi\), where \(a\) and \(b\) are real numbers.

Understanding imaginary numbers is key to navigating equations that initially seem to have no solution, opening up a broader mathematical world of complex numbers.

Square Roots of Negative Numbers

Taking the square root of a negative number seemed impossible with just real numbers until the introduction of the imaginary unit \(i\). The square root of a negative number is expressed as a multiple of \(i\). For example, if we need to solve \(\sqrt{-16}\), we use the property of \(i\) to write the solution as \(4i\). This is because \((4i)^2 = 16i^2 = 16(-1) = -16\).

Here's how you can handle square roots of negative numbers in general:

• Identify the negative number inside the square root, e.g., \(\sqrt{-n}\).
• Write it as \(\sqrt{n} \cdot \sqrt{-1}\).
• Replace \(\sqrt{-1}\) with \(i\), resulting in \(\sqrt{n}\cdot i\).

This process allows you to solve equations like \(x^2 + c = 0\) where \(c\) is a positive constant, converting potential impasse into a solution using complex numbers. Learning how these concepts interplay not only helps in solving such equations but also enriches your understanding of how mathematics extends beyond the real number limits.