Question

Find the discriminant of \(2 x^{2}-5 x-8=0\). Then identify the number of real solutions of the equation.

Short answer

The discriminant is 89. There are 2 distinct real solutions.

Step-by-step solution

- Identify coefficients

Given the quadratic equation in the form of \[ax^2 + bx + c = 0\], identify the coefficients: \(a\), \(b\), and \(c\). For the equation \(2x^2 - 5x -8 = 0\): \(a = 2\), \(b = -5\), and \(c = -8\).

- Write the discriminant formula

The discriminant of a quadratic equation is given by the formula: \(\Delta = b^2 - 4ac\).

- Substitute the coefficients into the discriminant formula

Substitute \(a = 2\), \(b = -5\), and \(c = -8\) into the formula. Calculate the discriminant: \[\Delta = (-5)^2 - 4(2)(-8)\].

- Simplify the expression

Perform the calculations step-by-step: \[\Delta = 25 + 64 = 89\]. The discriminant is 89.

- Determine the number of real solutions

Analyze the discriminant to determine the number of real solutions: - If \(\Delta > 0\), there are 2 distinct real solutions. - If \(\Delta = 0\), there is 1 real solution. - If \(\Delta < 0\), there are no real solutions. Since \(\Delta = 89 > 0\), there are 2 distinct real solutions.

Key concepts

quadratic equation

A quadratic equation is a second-degree polynomial usually written in the form \(ax^2 + bx + c = 0\). Here, \(a\), \(b\), and \(c\) are constants, and \(x\) is the variable. The coefficient \(a\) must not be zero, because if it were, the equation would become linear rather than quadratic. Quadratic equations appear in various real-world contexts, such as physics, engineering, and economics.
To solve a quadratic equation, we often use methods like factoring, completing the square, or the quadratic formula. The quadratic formula is particularly useful because it can solve any quadratic equation, regardless of whether it can be factored easily.
The general form of the quadratic formula is: \[x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}\].
This formula not only helps find the solutions or roots of the equation but also involves the discriminant, which plays a crucial role in determining the nature of the solutions.

discriminant

The discriminant of a quadratic equation is a special value that tells us about the nature of the roots without actually solving the equation. It is represented by the symbol \(\Delta\)_and is part of the quadratic formula.
For any quadratic equation of the form \(ax^2 + bx + c = 0\), the discriminant \(\Delta\) is calculated using the formula: \[\Delta = b^2 - 4ac\].
Here is a quick summary of what the discriminant reveals:

• If \(\Delta > 0\), the equation has two distinct real solutions.
• If \(\Delta = 0\), the equation has exactly one real solution (also known as a repeated or double root).
• If \(\Delta < 0\), the equation has no real solutions but two complex solutions.

For example, in the equation \(2x^2 - 5x - 8 = 0\), replacing \(a\), \(b\), and \(c\) into the formula gives us: \[\Delta = (-5)^2 - 4(2)(-8) = 25 + 64 = 89\],
which means \(\Delta\) is positive, indicating there are two distinct real solutions.

real solutions

Real solutions of a quadratic equation are the values of \(x\) that satisfy the equation and are real numbers. The discriminant \(\Delta\) helps us understand the number and nature of these solutions.
After calculating the discriminant:

• If \(\Delta > 0\), the quadratic equation has two distinct real solutions, meaning the parabola intersects the x-axis at two points.
• If \(\Delta = 0\), the quadratic equation has exactly one real solution, meaning the parabola touches the x-axis at one point.
• If \(\Delta < 0\), there are no real solutions, and the parabola does not intersect the x-axis. Instead, it has two complex solutions involving imaginary numbers.

In our example, the discriminant was calculated as \(89\), which is greater than 0. This means that the equation \(2x^2 - 5x - 8 = 0\) has two distinct real solutions. This is confirmed by observing the graph of the parabola, which would cross the x-axis at two different points.
Understanding whether a quadratic equation has real or complex solutions is essential since it provides insight into the behavior of the function represented by the equation.