Verify the Equality: (y+9)(2y-2) = 2y²-20y+18

Polynomial Expansion with Error Analysis

Is equality correct?

(y+9)(2y2)=2y220y+18 (y+9)(2y-2)=2y^2-20y+18

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:00 Are the expressions equal?
00:03 Let's properly open parentheses, multiply each factor by each factor
00:25 Let's calculate the products
00:43 Let's group the factors
00:49 Let's compare the expression terms, we'll see they're different
00:53 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

Is equality correct?

(y+9)(2y2)=2y220y+18 (y+9)(2y-2)=2y^2-20y+18

2

Step-by-step solution

To determine the correctness of the equation (y+9)(2y2)=2y220y+18 (y+9)(2y-2)=2y^2-20y+18 , follow these steps:

  • Step 1: Expand the left-hand side expression using the distributive property.

Start by applying the distributive property:
(y+9)(2y2)=y2y+y(2)+92y+9(2)(y + 9)(2y - 2) = y \cdot 2y + y \cdot (-2) + 9 \cdot 2y + 9 \cdot (-2)

  • Step 2: Calculate each term.

y2y=2y2y \cdot 2y = 2y^2
y(2)=2yy \cdot (-2) = -2y
92y=18y9 \cdot 2y = 18y
9(2)=189 \cdot (-2) = -18

  • Step 3: Combine the terms.

Now, combine the terms:
2y22y+18y182y^2 - 2y + 18y - 18

  • Step 4: Simplify the expression.

This simplifies to:
2y2+16y182y^2 + 16y - 18

  • Step 5: Compare with the right-hand side.

The expression 2y2+16y182y^2 + 16y - 18 does not match the right-hand side 2y220y+182y^2 - 20y + 18.

Therefore, the original expression is not correct as given. The discrepancy appears to be in the linear terms. If we adjust one factor in the left-hand side, for example changing y+9y + 9 to y9y - 9, we would get:

(y9)(2y2)=2y220y+18(y - 9)(2y - 2) = 2y^2 - 20y + 18, which would match the right side correctly.

Hence, the correct statement is: No, it must be (y9) (y-9) instead of (y+9) (y+9) .

3

Final Answer

No, it must be (y9) (y-9) instead of (y+9) (y+9)

Key Points to Remember

Essential concepts to master this topic
  • Distributive Property: Each term in first binomial multiplies every term in second
  • FOIL Method: (y+9)(2y-2) = 2y² - 2y + 18y - 18 = 2y² + 16y - 18
  • Compare Results: Check if expanded form matches given expression exactly ✓

Common Mistakes

Avoid these frequent errors
  • Assuming the equation is correct without expanding
    Don't just accept (y+9)(2y-2) = 2y²-20y+18 without checking! This leads to wrong conclusions about polynomial relationships. Always expand the left side completely using FOIL or distributive property, then compare coefficients term by term.

Practice Quiz

Test your knowledge with interactive questions

\( (3+20)\times(12+4)= \)

FAQ

Everything you need to know about this question

How do I expand (y+9)(2y-2) step by step?

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Use FOIL: First terms (y×2y = 2y²), Outer terms (y×(-2) = -2y), Inner terms (9×2y = 18y), Last terms (9×(-2) = -18). Then combine: 2y22y+18y18=2y2+16y18 2y^2 - 2y + 18y - 18 = 2y^2 + 16y - 18

Why doesn't my expansion match the given right side?

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Your expansion 2y2+16y18 2y^2 + 16y - 18 is correct! The given equation is wrong because the right side has 20y -20y instead of +16y +16y , and +18 +18 instead of 18 -18 .

What should the left side be to make the equation true?

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To get 2y220y+18 2y^2 - 20y + 18 , you need (y-9)(2y-2). Notice the sign change from +9 to -9. Try expanding this to verify!

How can I check if two polynomial expressions are equal?

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Method 1: Expand both sides and compare coefficients. Method 2: Substitute several values for the variable - if they give different results, the expressions aren't equal.

What's the difference between expanding and factoring?

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Expanding means going from factored form like (y+9)(2y-2) to standard form like 2y2+16y18 2y^2 + 16y - 18 . Factoring is the reverse - going from standard form back to factors.

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