Complete the Square: Fill in the Blanks for (x+?)^2 = x^2 + ? + 25

Perfect Square Trinomials with Constant Terms

Fill in the blanks:

(x+?)2=x2+?+25 (x+?)^2=x^2+?+25

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:00 Complete the missing
00:03 Let's mark the unknown with A
00:11 Let's use the shortened multiplication formulas to open the parentheses
00:19 Let's compare the coefficients and solve for A
00:31 Let's substitute and solve
00:42 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

Fill in the blanks:

(x+?)2=x2+?+25 (x+?)^2=x^2+?+25

2

Step-by-step solution

To solve this problem, we'll use the formula for the square of a sum, (a+b)2=a2+2ab+b2(a+b)^2 = a^2 + 2ab + b^2. This will help us determine the missing components in the expression.

The expression given is (x+?)2=x2+?+25(x+?)^2 = x^2 + ? + 25.

First, match it to the expanded form:

(x+b)2=x2+2bx+b2(x+b)^2 = x^2 + 2bx + b^2.

According to the problem, the expanded form is x2+?+25x^2 + ? + 25. This means b2=25b^2 = 25, so:
b2=25 b^2 = 25
Therefore, b=5b = 5 or b=5b = -5. For simplicity, let's choose b=5b = 5.

Now, calculate 2bx2bx:
2bx=2×5×x=10x 2bx = 2 \times 5 \times x = 10x

Substituting bb into the equation, we have:

(x+5)2=x2+10x+25(x+5)^2 = x^2 + 10x + 25.

Thus, the missing numbers are 55 and 10x10x.

Therefore, the solution to the problem is 5,10x 5, 10x .

3

Final Answer

5,10x 5,10x

Key Points to Remember

Essential concepts to master this topic
  • Formula: (a+b)2=a2+2ab+b2 (a+b)^2 = a^2 + 2ab + b^2 for perfect squares
  • Technique: From b2=25 b^2 = 25 , find b = 5, then 2bx = 10x
  • Check: Expand (x+5)2=x2+10x+25 (x+5)^2 = x^2 + 10x + 25

Common Mistakes

Avoid these frequent errors
  • Finding the square root incorrectly
    Don't assume the first blank is 25=5 \sqrt{25} = 5 without checking the middle term! This gives wrong middle coefficients like 125x \sqrt{125}x . Always use the formula: if b2=25 b^2 = 25 , then b = 5 and the middle term is 2bx = 10x.

Practice Quiz

Test your knowledge with interactive questions

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

\( (x+y)^2 \)

FAQ

Everything you need to know about this question

Why can't the first blank be 125 \sqrt{125} ?

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Because we need both blanks to work together! If the first blank were 125 \sqrt{125} , the constant term would be (125)2=125 (\sqrt{125})^2 = 125 , not 25.

How do I know which sign to use for b?

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Since b2=25 b^2 = 25 , b could be +5 or -5. The problem shows (x+?) (x+?) with a plus sign, so we use b = +5.

What if I forgot the perfect square formula?

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Remember: (a+b)2=a2+2ab+b2 (a+b)^2 = a^2 + 2ab + b^2 . The middle term is always twice the product of the two terms being squared.

Can I work backwards from the expanded form?

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Yes! From x2+?+25 x^2 + ? + 25 , you know the constant is b2=25 b^2 = 25 , so b = 5. Then the middle term must be 2(x)(5)=10x 2(x)(5) = 10x .

Why is the middle term 10x and not 5x?

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The formula requires doubling the product: 2ab=2(x)(5)=10x 2ab = 2(x)(5) = 10x . Don't forget the coefficient 2!

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