Root Formula: Solve x² + 7¾x - 2 Using Step-by-Step Method

Quadratic Factoring with Mixed Number Coefficients

Use the root formula and extract the trinomial

x2+734x2 x^2+7\frac{3}{4}x-2

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:06 We're going to factorize this trinomial by using the roots formula.
00:10 First, let's identify the coefficients. This is our starting point.
00:19 Next, we'll use the roots formula to explore possible solutions.
00:30 Now we'll substitute the right values to find these solutions.
00:41 Let's go ahead and calculate the root. Almost there!
00:54 We'll look for two possible solutions using addition and subtraction.
00:59 These solutions help us construct the original trinomial.
01:05 Let's determine what zeros these solutions create.
01:10 These zeros will be our trinomial's factors.
01:16 And that's the solution to our problem! Great job everyone!

Step-by-step written solution

Follow each step carefully to understand the complete solution
1

Understand the problem

Use the root formula and extract the trinomial

x2+734x2 x^2+7\frac{3}{4}x-2

2

Step-by-step solution

The quadratic equation given is:

x2+734x2=0 x^2 + 7\frac{3}{4}x - 2 = 0

First, let's rewrite the coefficient b b as a decimal for simplicity:

b=734=7.75 b = 7\frac{3}{4} = 7.75

Given a=1 a = 1 , b=7.75 b = 7.75 , and c=2 c = -2 , we apply the quadratic formula:

x=b±b24ac2a x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}

Calculate the discriminant:

Discriminant=b24ac=(7.75)24×1×2 \text{Discriminant} = b^2 - 4ac = (7.75)^2 - 4 \times 1 \times -2

=60.0625+8=68.0625 = 60.0625 + 8 = 68.0625

Now, find the roots by plugging into the quadratic formula:

x=7.75±68.06252 x = \frac{-7.75 \pm \sqrt{68.0625}}{2}

Calculate the square root:

68.0625=8.25 \sqrt{68.0625} = 8.25

Find the roots:

x1=7.75+8.252=0.52=0.25 x_1 = \frac{-7.75 + 8.25}{2} = \frac{0.5}{2} = 0.25

x2=7.758.252=162=8 x_2 = \frac{-7.75 - 8.25}{2} = \frac{-16}{2} = -8

Thus, the factored form of the trinomial can be written using these roots:

(xx1)(xx2)=(x0.25)(x+8) (x - x_1)(x - x_2) = (x - 0.25)(x + 8)

Rewriting with fractional representations:

(x14)(x+8) (x - \frac{1}{4})(x + 8)

Thus, the trinomial can be expressed as:

(x+8)(x14) (x + 8)(x - \frac{1}{4})

Comparing with the options provided, the correct answer is:

(x+8)(x14) \boxed{(x + 8)(x - \frac{1}{4})}

3

Final Answer

(x+8)(x14) (x+8)(x-\frac{1}{4})

Key Points to Remember

Essential concepts to master this topic
  • Formula: Use quadratic formula when coefficients are mixed numbers
  • Technique: Convert 734 7\frac{3}{4} to 7.75 before calculating discriminant
  • Check: Expand factored form back to original trinomial x2+734x2 x^2 + 7\frac{3}{4}x - 2

Common Mistakes

Avoid these frequent errors
  • Converting mixed numbers incorrectly to decimals
    Don't write 734 7\frac{3}{4} as 7.3 or 7.34 = wrong discriminant and roots! Mixed numbers need proper conversion: 7 + 3/4 = 7.75. Always convert mixed numbers to improper fractions or correct decimals first.

Practice Quiz

Test your knowledge with interactive questions

a = Coefficient of x²

b = Coefficient of x

c = Coefficient of the independent number


what is the value of \( a \) in the equation

\( y=3x-10+5x^2 \)

FAQ

Everything you need to know about this question

Why should I convert the mixed number to a decimal?

+

Converting 734 7\frac{3}{4} to 7.75 makes calculations easier! You can also work with the improper fraction 314 \frac{31}{4} , but decimals are often simpler for the quadratic formula.

How do I know which factored form is correct?

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Always expand your answer and check if you get the original trinomial. If (x+8)(x14) (x+8)(x-\frac{1}{4}) expands to x2+734x2 x^2 + 7\frac{3}{4}x - 2 , it's correct!

What if my discriminant doesn't give a perfect square?

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If b24ac b^2 - 4ac isn't a perfect square, the trinomial cannot be factored using integers or simple fractions. In this problem, 68.0625 = 8.25², so it factors nicely.

Can I use factoring by grouping instead?

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Factoring by grouping works best with integer coefficients. With mixed numbers like 734 7\frac{3}{4} , the quadratic formula is more reliable and straightforward.

Why is the answer written as (x + 8)(x - 1/4) and not the other way?

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The order doesn't matter for multiplication! (x+8)(x14) (x + 8)(x - \frac{1}{4}) equals (x14)(x+8) (x - \frac{1}{4})(x + 8) . Choose whichever form matches your answer choices.

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