Solve the Rational Equation: (x³+1)/(x-1)² = x+4

Rational Equations with Polynomial Multiplication

Solve the following equation:

x3+1(x1)2=x+4 \frac{x^3+1}{(x-1)^2}=x+4

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:00 Solve
00:08 Multiply to eliminate the fraction
00:24 Use the distributive property of multiplication to expand the parentheses
00:47 Calculate the multiplication
00:55 Make sure to properly open parentheses
01:04 Each term in the first parentheses multiplies each term in the second parentheses
01:25 Reduce where possible
01:32 Collect like terms
01:42 Arrange the equation so that one side equals 0
01:50 Use the quadratic formula to find possible solutions
02:05 Calculate the multiplication
02:20 Solve for the positive option
02:26 This is one solution
02:29 Now solve for the negative option
02:33 This is the second solution
02:37 Note the domain restrictions, the denominator must not equal 0
02:47 And this is the solution to the problem

Step-by-step written solution

Follow each step carefully to understand the complete solution
1

Understand the problem

Solve the following equation:

x3+1(x1)2=x+4 \frac{x^3+1}{(x-1)^2}=x+4

2

Step-by-step solution

To solve this equation, we follow these steps:

  • Step 1: Multiply both sides by (x1)2(x-1)^2 to eliminate the fraction.
  • Step 2: Expand and simplify both sides of the equation.
  • Step 3: Rearrange the equation to form a polynomial equal to zero.
  • Step 4: Solve the resulting polynomial using factorization or the quadratic formula.

Now, let's execute these steps:

Step 1: Multiply both sides by (x1)2(x-1)^2:
(x3+1)=(x+4)(x1)2(x^3 + 1) = (x + 4)(x - 1)^2

Step 2: Expand the right side:
(x+4)(x22x+1)=x(x22x+1)+4(x22x+1) (x + 4)(x^2 - 2x + 1) = x(x^2 - 2x + 1) + 4(x^2 - 2x + 1)

Calculating each part yields:
x(x22x+1)=x32x2+x x(x^2 - 2x + 1) = x^3 - 2x^2 + x
4(x22x+1)=4x28x+4 4(x^2 - 2x + 1) = 4x^2 - 8x + 4

Add these together:
x32x2+x+4x28x+4=x3+2x27x+4 x^3 - 2x^2 + x + 4x^2 - 8x + 4 = x^3 + 2x^2 - 7x + 4

Step 3: Combine terms and rearrange:
x3+1=x3+2x27x+4 x^3 + 1 = x^3 + 2x^2 - 7x + 4

Simplify by cancelling x3x^3 from both sides:
1=2x27x+4 1 = 2x^2 - 7x + 4

Move 1 to the right side:
0=2x27x+3 0 = 2x^2 - 7x + 3

Step 4: Solve the quadratic equation 2x27x+3=0 2x^2 - 7x + 3 = 0 .

Using the quadratic formula, x=b±b24ac2a x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a} , where a=2 a = 2 , b=7 b = -7 , and c=3 c = 3 .

Calculate the discriminant:
b24ac=(7)2423=4924=25 b^2 - 4ac = (-7)^2 - 4 \cdot 2 \cdot 3 = 49 - 24 = 25

Now plug into the quadratic formula:
x=7±254 x = \frac{7 \pm \sqrt{25}}{4}

Simplify:
x=7±54 x = \frac{7 \pm 5}{4}

Two solutions arise:
x=124=3 x = \frac{12}{4} = 3 and x=24=12 x = \frac{2}{4} = \frac{1}{2}

Since x=1 x = 1 would make the denominator zero, it is not a valid solution for the original equation.

Therefore, the solution to the problem is x=3 x = 3 or x=12 x = \frac{1}{2} .

3

Final Answer

x=3,12 x=3,\frac{1}{2}

Key Points to Remember

Essential concepts to master this topic
  • Rule: Multiply both sides by the denominator to eliminate fractions
  • Technique: Expand (x+4)(x1)2 (x+4)(x-1)^2 to get x3+2x27x+4 x^3 + 2x^2 - 7x + 4
  • Check: Substitute x=3 x = 3 : 284=7 \frac{28}{4} = 7

Common Mistakes

Avoid these frequent errors
  • Forgetting to check for excluded values
    Don't skip checking if x=1 x = 1 makes the denominator zero = invalid solution! This critical step prevents division by zero errors. Always identify restricted values from the original denominator before solving.

Practice Quiz

Test your knowledge with interactive questions

Determine if the simplification shown below is correct:

\( \frac{7}{7\cdot8}=8 \)

FAQ

Everything you need to know about this question

Why can't x = 1 be a solution even if it satisfies the simplified equation?

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Because x=1 x = 1 makes the denominator (x1)2=0 (x-1)^2 = 0 , which means division by zero. The original equation becomes undefined, so this value must be excluded from any solution set.

How do I expand (x+4)(x-1)² correctly?

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First expand (x1)2=x22x+1 (x-1)^2 = x^2 - 2x + 1 , then multiply by (x+4) (x+4) . Use distribution: x(x22x+1)+4(x22x+1) x(x^2-2x+1) + 4(x^2-2x+1) to get the final result.

What if I get a cubic equation instead of quadratic?

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Don't worry! In this problem, the x3 x^3 terms cancel out when you subtract, leaving a quadratic. Always combine like terms and simplify before assuming you need to solve a cubic.

Can I use factoring instead of the quadratic formula?

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Yes! For 2x27x+3=0 2x^2 - 7x + 3 = 0 , you can factor as (2x1)(x3)=0 (2x-1)(x-3) = 0 . This gives the same solutions: x=12 x = \frac{1}{2} and x=3 x = 3 .

How do I verify my solutions are correct?

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Substitute each solution back into the original equation. For x=3 x = 3 : 27+1(31)2=284=7 \frac{27+1}{(3-1)^2} = \frac{28}{4} = 7 and 3+4=7 3+4 = 7

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