Problem 51 - Brief Applied Calculus

Question

Solve each equation by factoring or the Quadratic Formula, as appropriate. $$ 3 x^{2}+12=0 $$

Step-by-Step Solution

Answer

The solutions are \( x = 2i \) and \( x = -2i \).

Step 1: Move Constant to the Other Side

Start by isolating the quadratic term. Subtract 12 from both sides of the equation to get:\[ 3x^2 = -12 \]

Step 2: Divide by the Coefficient of the Quadratic Term

Divide every term by the coefficient of \( x^2 \), which is 3, to simplify the equation:\[ x^2 = -4 \]

Step 3: Solve for x Using Square Roots

Take the square root of both sides to solve for \( x \). Remember that taking the square root of a negative number involves imaginary numbers. Thus, the solutions are:\[ x = \pm \sqrt{-4} \]This simplifies to:\[ x = \pm 2i \]

Key Concepts

Factoring

Factoring is one of the classic methods for solving quadratic equations. The process involves rewriting the quadratic expression as a product of simpler expressions, typically binomials. For instance, if you have an equation like \( ax^2 + bx + c = 0 \), factoring it may look like \((px + q)(rx + s) = 0\). When working with factoring, the key is to find two numbers that multiply to give the constant term \(c\) and add to give the coefficient \(b\) of the linear term.In some cases, just like in our exercise, factoring might not be applicable directly, especially when dealing with a negative constant on the simplified side or when complex numbers come into play. Thus, it's crucial to recognize when factoring is not straightforward and when another method, like the quadratic formula, must be used.

Quadratic Formula

The quadratic formula is an all-encompassing tool for finding the solutions to any quadratic equation, which takes the form of \( ax^2 + bx + c = 0 \). The formula itself is:\[ x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a} \]This formula works universally, regardless of whether the roots are real or complex. By calculating the discriminant \( b^2 - 4ac \), you can determine the nature of the roots:

• If the discriminant is positive, there are two distinct real roots.
• If it's zero, there is exactly one real root (a repeated root).
• If it's negative, the roots are complex or imaginary.

In our example, should we choose to apply the quadratic formula, we would identify \( a = 3 \), \( b = 0 \), and \( c = 12 \). Plugging these into the quadratic formula would confirm the imaginary roots we calculated using another method.

Imaginary Numbers

Imaginary numbers are used to deal with situations where you need to find the square root of negative numbers. By definition, the unit imaginary number is \( i \), which is defined as \( i = \sqrt{-1} \). This allows us to extend the number system and solve equations that have no real-number solutions.In the exercise, we encountered an expression where \( x^2 = -4 \). Taking the square root of both sides gives us \( x = \pm \sqrt{-4} \). Applying the rule for square roots of negative numbers, this simplifies to \( x = \pm 2i \), meaning the solutions are purely imaginary numbers.Imaginary numbers become essential in various fields, including engineering and physics, because they provide a way to mathematically represent systems and problems that include oscillatory behaviors or wave functions that wouldn't otherwise be expressible using only real numbers. In summary, understanding how to work with \( i \) is crucial for solving and analyzing a broader class of equations.