All Precalculus Resources
Example Questions
Example Question #11 : Solving Quadratic Equations
Solve the quadratic equation for .
None of the other answers.
None of the other answers.
There are two solutions; .
We proceed as follows.
Add to both sides.
Take the square root of both sides, remember to introduce plus/minus on the right side since you are introducing a square root into your work.
Add to both sides.
Example Question #12 : Solving Quadratic Equations
Solve the quadratic equation for .
Use the quadratic formula.
None of the other answers.
For any quadtratic equation of the form , the quadratic formula is
Plugging in our given values we have:
Example Question #6 : Solve A Quadratic Equation
Find the roots of the equation.
Use either the quadratic formula or factoring to solve the quadratic equation.
Using factoring, we want to find which factors of six when multiplied with the factors of two and then added together result in negative one.
Using the quadratic formula,
let
Example Question #7 : Solve A Quadratic Equation
Solve .
To solve this equation, use trial and error to factor it. Since the leading coefficient is , there is only one way to get , so that is helpful reminder. Once it's properly factored, you get: . Then, set both of those expressions equal to to get your roots: .
Example Question #1 : Find Roots Of Quadratic Equation Using Discriminant
True or false: for a quadratic function of form ax2 + bx + c = 0, if the discriminant b2 - 4ac = 0, there is exactly one real root.
True
False
True
This is true. The discriminant b2 - 4ac is the part of the quadratic formula that lives inside of a square root function. As you plug in the constants a, b, and c into b2 - 4ac and evaluate, three cases can happen:
b2 - 4ac > 0
b2 - 4ac = 0
b2 - 4ac < 0
In the first case, having a positive number under a square root function will yield a result that is a positive number answer. However, because the quadratic function includes , this scenario yields two real results.
In the middle case (the case of our example), . Going back to the quadratic formula , you can see that when everything under the square root is simply 0, then you get only , which is why you have exactly one real root.
For the final case, if b2 - 4ac < 0, that means you have a negative number under a square root. This means that you will not have any real roots of the equation; however, you will have exactly two imaginary roots of the equation.
Example Question #2 : Find Roots Of Quadratic Equation Using Discriminant
True or false: for a quadratic function of form ax2 + bx + c = 0, if the discriminant b2 - 4ac > 0, there are exactly 2 distinct real roots of the equation.
True
False
True
This is true. The discriminant b2 - 4ac is the part of the quadratic formula that lives inside of a square root function. As you plug in the constants a, b, and c into b2 - 4ac and evaluate, three cases can happen:
b2 - 4ac > 0
b2 - 4ac = 0
b2 - 4ac < 0
In the first case (the case of our example), having a positive number under a square root function will yield a result that is a positive number answer. However, because the quadratic function includes , this scenario yields two real results.
In the middle case, . Going back to the quadratic formula , you can see that when everything under the square root is simply 0, then you get only , which is why you have exactly one real root.
For the final case, if b2 - 4ac < 0, that means you have a negative number under a square root. This means that you will not have any real roots of the equation; however, you will have exactly two imaginary roots of the equation.
Example Question #3 : Find Roots Of Quadratic Equation Using Discriminant
True or false: for a quadratic function of form ax2 + bx + c = 0, if the discriminant b2 - 4ac < 0, there are exactly two distinct real roots.
True
False
False
This is false. The discriminant b2 - 4ac is the part of the quadratic formula that lives inside of a square root function. As you plug in the constants a, b, and c into b2 - 4ac and evaluate, three cases can happen:
b2 - 4ac > 0
b2 - 4ac = 0
b2 - 4ac < 0
In the first case, having a positive number under a square root function will yield a result that is a positive number answer. However, because the quadratic function includes , this scenario yields two real results.
In the middle case, . Going back to the quadratic formula , you can see that when everything under the square root is simply 0, then you get only , which is why you have exactly one real root.
For the final case (the case of our example), if b2 - 4ac < 0, that means you have a negative number under a square root. This means that you will not have any real roots of the equation; however, you will have exactly two imaginary roots of the equation.
Example Question #1 : Find Roots Of Quadratic Equation Using Discriminant
Use the formula b2 - 4ac to find the discriminant of the following equation: 4x2 + 19x - 5 = 0.
Then state how many roots it has, and whether they are real or imaginary. Finally, use the quadratic function to find the exact roots of the equation.
Discriminant: 0
One real root:
Discriminant: 281
Two imaginary roots:
Discriminant: 441
Two real roots: or
Discriminant: 441
Two real roots: or
Discriminant: 281
Two imaginary roots:
Discriminant: 441
Two real roots: or
In the above equation, a = 4, b = 19, and c = -5. Therefore:
b2 - 4ac = (19)2 - 4(4)(-5) = 361 + 80 = 441.
When the discriminant is greater than 0, there are two distinct real roots. When the discriminant is equal to 0, there is exactly one real root. When the discriminant is less than zero, there are no real roots, but there are exactly two distinct imaginary roots. In this case, we have two real roots.
Finally, we use the quadratic function to find these exact roots. The quadratic function is:
Plugging in our values of a, b, and c, we get:
This simplifies to:
which simplifies to
which gives us two answers:
or
These values of x are the two distinct real roots of the given equation.
Example Question #2 : Find Roots Of Quadratic Equation Using Discriminant
Use the formula b2 - 4ac to find the discriminant of the following equation: 4x2 + 12x + 10 = 0.
Then state how many roots it has, and whether they are real or imaginary. Finally, use the quadratic function to find the exact roots of the equation.
Discriminant: 304
Types of Roots: Two distinct real roots
Exact Roots:
Discriminant: 304
Types of Roots: Two distinct real roots
Exact Roots:
Discriminant: -16
Types of Roots: No real roots; 2 distinct imaginary roots
Exact Roots:
Discriminant: -16
Types of Roots: No real roots; 2 distinct imaginary roots
Exact Roots:
Discriminant: 16
Types of Roots: Two distinct real roots
Exact Roots: -1, -2
Discriminant: -16
Types of Roots: No real roots; 2 distinct imaginary roots
Exact Roots:
In the above equation, a = 4, b = 12, and c = 10. Therefore:
b2 - 4ac = (12)2 - 4(4)(10) = 144 - 160 = -16.
When the discriminant is greater than 0, there are two distinct real roots. When the discriminant is equal to 0, there is exactly one real root. When the discriminant is less than zero, there are no real roots, but there are exactly two distinct imaginary roots. In this case, we have two distinct imaginary roots.
Finally, we use the quadratic function to find these exact roots. The quadratic function is:
Plugging in our values of a, b, and c, we get:
This simplifies to:
In other words, our two distinct imaginary roots are and
Example Question #4 : Find Roots Of Quadratic Equation Using Discriminant
Use the formula b2 - 4ac to find the discriminant of the following equation: -3x2 + 6x - 3 = 0.
Then state how many roots it has, and whether they are real or imaginary. Finally, use the quadratic function to find the exact roots of the equation.
Discriminant: 0
One real root: x = -1
Discriminant: 0
One real root: x = 1
Discriminant: 72
Two distinct real roots:
Discriminant: 72
Two distinct real roots:
Discriminant: -72
Two distinct imaginary roots:
Discriminant: 0
One real root: x = 1
In the above equation, a = -3, b = 6, and c = -3. Therefore:
b2 - 4ac = (6)2 - 4(-3)(-3) = 36 - 36 = 0.
When the discriminant is greater than 0, there are two distinct real roots. When the discriminant is equal to 0, there is exactly one real root. When the discriminant is less than zero, there are no real roots, but there are exactly two distinct imaginary roots. In this case, there is exactly one real root.
Finally, we use the quadratic function to find these exact root. The quadratic formula is:
Plugging in our values of a, b, and c, we get:
This simplifies to:
which simplifies to
which gives us one answer: x = 1
This value of x is the one distinct real root of the given equation.
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