Solve (x+4)(3x-1/4) = 3(x²+5): Complete Quadratic Equation Guide

Quadratic Equations with Mixed Number Solutions

(x+4)(3x14)=3(x2+5) (x+4)(3x-\frac{1}{4})=3(x^2+5)

x=? x=?

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:00 Solve
00:04 Open parentheses properly and multiply each factor by each factor
00:25 Open parentheses properly and multiply by each factor
00:40 Solve each multiplication separately
00:57 Simplify what's possible
01:01 Collect terms
01:13 Isolate the unknown X
01:25 Convert from number and fraction to fraction
01:30 Calculate the numerator multiplication
01:34 Multiply by denominator to eliminate the fraction
01:48 Isolate the unknown X
01:56 Break down 64 into 47 plus 17
02:04 Break down one fraction into a whole number and remainder
02:14 And this is the solution to the question

Step-by-step written solution

Follow each step carefully to understand the complete solution
1

Understand the problem

(x+4)(3x14)=3(x2+5) (x+4)(3x-\frac{1}{4})=3(x^2+5)

x=? x=?

2

Step-by-step solution

To solve the equation (x+4)(3x14)=3(x2+5) (x+4)(3x-\frac{1}{4}) = 3(x^2+5) , follow these steps:

  • Step 1: Expand the left side of the equation
    (x+4)(3x14)(x + 4)(3x - \frac{1}{4})

Using the distributive property:

x(3x)+x(14)+4(3x)+4(14) x(3x) + x(-\frac{1}{4}) + 4(3x) + 4(-\frac{1}{4})

=3x2x4+12x1 = 3x^2 - \frac{x}{4} + 12x - 1

  • Step 2: Simplify the expanded left side
    Combine like terms:

3x2+(12xx4)1 3x^2 + \left(12x - \frac{x}{4}\right) - 1

Convert x4\frac{x}{4} to a common denominator: 48x4x4=47x4\frac{48x}{4} - \frac{x}{4} = \frac{47x}{4}

Thus, the left side is: 3x2+47x41 3x^2 + \frac{47x}{4} - 1

  • Step 3: Simplify the right side
    3(x2+5)3(x^2 + 5)

=3x2+15 = 3x^2 + 15

  • Step 4: Set the simplified expressions equal and solve for x x

3x2+47x41=3x2+15 3x^2 + \frac{47x}{4} - 1 = 3x^2 + 15

Subtract 3x23x^2 from both sides:

47x41=15 \frac{47x}{4} - 1 = 15

Add 1 to both sides:

47x4=16 \frac{47x}{4} = 16

Multiply both sides by 4 to clear the fraction:

47x=64 47x = 64

  • Step 5: Solve for x x

x=6447 x = \frac{64}{47}

Express 6447\frac{64}{47} as a mixed number:

x=11747 x = 1\frac{17}{47}

Therefore, the solution to the equation is x=11747 x = 1\frac{17}{47} .

3

Final Answer

11747 1\frac{17}{47}

Key Points to Remember

Essential concepts to master this topic
  • Expansion: Use FOIL to multiply binomials like (x+4)(3x-1/4)
  • Technique: Combine like terms: 12x - x/4 = 48x/4 - x/4 = 47x/4
  • Check: Substitute x = 64/47 back into original equation to verify equality ✓

Common Mistakes

Avoid these frequent errors
  • Incorrectly combining fractional and whole number terms
    Don't add 12x and -x/4 as 11x or 12x-1/4x = wrong coefficient! This creates an incorrect linear term. Always convert to common denominators: 12x = 48x/4, then 48x/4 - x/4 = 47x/4.

Practice Quiz

Test your knowledge with interactive questions

Solve for X:

\( 3x=18 \)

FAQ

Everything you need to know about this question

Why does the x² term cancel out on both sides?

+

After expanding both sides, we get 3x2 3x^2 on the left and 3x2 3x^2 on the right. When we subtract 3x2 3x^2 from both sides, they cancel completely, leaving us with a linear equation!

How do I convert 12x - x/4 to a single fraction?

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Convert 12x to fourths: 12x=48x4 12x = \frac{48x}{4} . Then subtract: 48x4x4=47x4 \frac{48x}{4} - \frac{x}{4} = \frac{47x}{4} . Always use the same denominator!

Why is the answer written as a mixed number?

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The fraction 6447 \frac{64}{47} is improper (numerator > denominator). Converting to mixed number form 11747 1\frac{17}{47} makes it easier to understand the size of the answer.

What if I made an error in the FOIL step?

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Double-check each term: x3x=3x2 x \cdot 3x = 3x^2 , x(14)=x4 x \cdot (-\frac{1}{4}) = -\frac{x}{4} , 43x=12x 4 \cdot 3x = 12x , and 4(14)=1 4 \cdot (-\frac{1}{4}) = -1 . Write each step clearly to avoid sign errors!

Can this type of equation have no solution?

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Yes! If after simplifying you get something like 0=5 0 = 5 (a false statement), there's no solution. But in this problem, we get a valid value for x.

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