Algebra II : Discriminants

Study concepts, example questions & explanations for Algebra II

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Example Questions

Example Question #11 : Discriminants

Use the discriminant to determine the number of unique zeros for the quadratic:

Possible Answers:

1 root

2 roots

0 roots

3 roots

Correct answer:

1 root

Explanation:

The discriminant is part of the quadratic formula. In the quadratic formula, 

The discriminant is the term:

If the discriminant is 0, there is only one real solution. This would be:

, since the our discriminant is gone.

If the discriminant is a positive number, then we have two real roots, the usual form of the quadratic equation:

Finally, if the discriminant is negative, we would be taking the square root of a negative number. This will give us no real zeros.

Plugging the numbers into the discriminant gives us:

The discriminant is zero, so there is only one root,

 

Example Question #11 : Discriminants

Use the discriminant to determine the number of real roots the function has:

Possible Answers:

The function has one real root

The function has two real roots

It is impossible to determine 

The function has no real roots

Correct answer:

The function has two real roots

Explanation:

Using the discriminant, which for a polynomial 

is equal to

,

we can determine the number of roots a polynomial has. If the discriminant is positive, then the polynomial has two real roots. If it is equal to zero, the polynomial has one real root. If it is negative, then the polynomial has two roots which are complex conjugates of one another.

For our function, we have

,

so when we plug these into the discriminant formula, we get

So, our polynomial has two real roots.

Example Question #13 : Discriminants

Find the discriminant of the following quadratic equation:

Possible Answers:

Correct answer:

Explanation:

The discriminant is found using the following formula:

For the particular function in question the variable are as follows.

Therefore:

Example Question #12 : Discriminants

Determine the number of real roots the given function has:

Possible Answers:

Two real roots

One real root

None of the other answers

No real roots

Correct answer:

One real root

Explanation:

To determine the amount of roots a given quadratic function has, we must find the discriminant, which for 

is equal to

If d is negative, then we have two roots that are complex conjugates of one another. If d is positive, than we have two real roots, and if d is equal to zero, then we have only one real root.

Using our function and the formula above, we get

Thus, the function has only one real root.

Example Question #15 : Discriminants

What is the discriminant of ?

Possible Answers:

Correct answer:

Explanation:

Write the formula for the discriminant.  This is the term inside the square root of the quadratic formula.

The given equation is already in the form of .

Substitute the terms into the formula.

The answer is:  

Example Question #16 : Discriminants

Determine the discriminant of the following parabola:  

Possible Answers:

Correct answer:

Explanation:

The polynomial is written in the form , where

Write the formula for the discriminant.  This is the term inside the square root value of the quadratic equation.

Substitute all the knowns into this equation.

The answer is:  

Example Question #17 : Discriminants

Describe the roots of this quadratic equation by evaluating the discriminant: 

Possible Answers:

Because the discriminant is positive, this quadratic will have two distinct and real solutions.

None of these

Because the discriminant is negative, this quadratic will have two complex roots.

Because the discriminant is negative, it will have two distinct and real solutions.

Because the discriminant equals 0, the quadratic will have one repeated solution. 

Correct answer:

Because the discriminant is negative, this quadratic will have two complex roots.

Explanation:

We use the quadratic formula to evaluate the types of roots, but it is not necessary to solve the whole equation. Simply look at the discriminant or square root part. 

Plug in the correct numbers in the discriminant and simplify. Do not take the square root.

Since  will be negative, this equation will have two complex solutions.

Discrimant<0= Two complex solutions

Discriminant>0= Two distinct and real solutions

Discriminant=0 = One repeated solution

Example Question #18 : Discriminants

What is the discriminant?  

Possible Answers:

Correct answer:

Explanation:

This equation is already in the form of .

Write the expression for the discriminant.  This is the term inside the square root of the quadratic equation.

Substitute the terms into the expression and solve.

The answer is:  

Example Question #19 : Discriminants

Determine the discriminant for:  

Possible Answers:

Correct answer:

Explanation:

Identify the coefficients for the polynomial .

Write the expression for the discriminant.  This is the expression inside the square root from the quadratic formula.

Substitute the numbers.

The answer is:  

Example Question #11 : Discriminants

Evaluate the discriminant given the parabola:  

Possible Answers:

Correct answer:

Explanation:

The discriminant is the term inside the square root of the quadratic equation.

Identify the values of each variable.  This corresponds to the coefficients of the quadratic in standard form:

Substitute these values into the expression to determine the discriminant.

The discriminant is:  

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