Solve the Quadratic Equation: x² + 32x = -256

Quadratic Equations with Perfect Square Trinomials

Solve for x:

x2+32x=256 x^2+32x=-256

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:06 Let's find the value of X.
00:09 First, rearrange the equation so one side equals zero.
00:24 Now, break down two fifty-six as sixteen squared.
00:30 Next, factor thirty-two into two times sixteen.
00:39 Use special formulas to find the factors in the brackets.
00:44 Then, isolate the variable X.
00:49 And that's how we find the solution to the problem.

Step-by-step written solution

Follow each step carefully to understand the complete solution
1

Understand the problem

Solve for x:

x2+32x=256 x^2+32x=-256

2

Step-by-step solution

To solve the quadratic equation x2+32x=256 x^2 + 32x = -256 , we will use the method of completing the square.

First, we rewrite the equation by moving all terms to one side:
x2+32x+256=0 x^2 + 32x + 256 = 0 .

Next, we complete the square for the expression x2+32x x^2 + 32x . We want to express it in the form (x+a)2 (x + a)^2 . To do this, take half of the coefficient of x x (which is 32), square it, and add and subtract the square inside the expression:
- Half of 32 is 16.
- Squaring 16 gives 256.
- Therefore, x2+32x=(x+16)2256 x^2 + 32x = (x + 16)^2 - 256 .

Substitute back into the equation:
(x+16)2256+256=0 (x + 16)^2 - 256 + 256 = 0
which simplifies to (x+16)2=0 (x + 16)^2 = 0 .

To find x x , solve the equation (x+16)2=0 (x + 16)^2 = 0 :
Taking the square root of both sides gives x+16=0 x + 16 = 0 .
Thus, x=16 x = -16 .

Therefore, the solution to the quadratic equation is x=16 x = -16 .

3

Final Answer

x=16 x=-16

Key Points to Remember

Essential concepts to master this topic
  • Rule: Move all terms to one side before completing the square
  • Technique: Take half of coefficient (32÷2=16), then square it: 16²=256
  • Check: Substitute x=-16: (-16)²+32(-16)=256-512=-256 ✓

Common Mistakes

Avoid these frequent errors
  • Forgetting to move constant term to one side first
    Don't try completing the square with x²+32x=-256 directly = messy calculations and wrong setup! You'll add 256 to the wrong side. Always move all terms to one side first: x²+32x+256=0.

Practice Quiz

Test your knowledge with interactive questions

Choose the expression that has the same value as the following:


\( (x+3)^2 \)

FAQ

Everything you need to know about this question

Why does this equation have only one solution instead of two?

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This quadratic equation has a repeated root because it forms a perfect square trinomial (x+16)2=0 (x+16)^2=0 . When a perfect square equals zero, there's only one solution: x=-16.

How do I know when to use completing the square vs other methods?

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Completing the square works for all quadratics, but it's especially useful when the coefficient of x2 x^2 is 1 and you can't factor easily. Try factoring first, then use this method!

What if the coefficient of x is odd instead of even?

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No problem! Take half anyway: if the coefficient is 7, then 72=3.5 \frac{7}{2} = 3.5 and (3.5)2=12.25 (3.5)^2 = 12.25 . The method works with any coefficient.

Why do we add and subtract the same number when completing the square?

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Adding and subtracting the same number keeps the equation balanced - we're essentially adding zero! This lets us create a perfect square trinomial without changing the equation's solutions.

Can I use the quadratic formula instead?

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Absolutely! The quadratic formula x=b±b24ac2a x = \frac{-b \pm \sqrt{b^2-4ac}}{2a} will give the same answer. With a=1, b=32, c=256, you'll get x=-16.

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