Is it necessary to expand the quantity before factoring the expression?

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In summary, we are asked to factor the expression 4a^2b^2 - 9(ab + c)^2 and we can do so by recognizing it as a difference of squares, resulting in the factors (2ab - 3(ab + c)) and (2ab + 3(ab + c)). While further simplification is not required, it is good practice to simplify whenever possible.
  • #1
mathdad
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Precalculus by David Cohen, 3rd Edition
Chapter 1, Section 1.3.
Question 29c.

Factor the expression.

4a^2b^2 - 9(ab + c)^2

Must I expand the quantity (ab + c) before factoring?
 
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  • #2
RTCNTC said:
Precalculus by David Cohen, 3rd Edition
Chapter 1, Section 1.3.
Question 29c.

Factor the expression.

4a^2b^2 - 9(ab + c)^2

Must I expand the quantity (ab + c) before factoring?

You need not

you get as $(2ab)^2 - (3(ab+c))^2$ difference of 2 squares and now you should be able to proceed
 
  • #3
(2ab)^2−(3(ab+c))^2

I will let 2ab = x and [3(ab + c)] = y.

x^2 - y^(2)

(x - y)(x + y)

Back-substitute now.

[(2ab - 3(ab + c)][(2ab + 3(ab + c)]

Correct?
 
  • #4
RTCNTC said:
(2ab)^2−(3(ab+c))^2

I will let 2ab = x and [3(ab + c)] = y.

x^2 - y^(2)

(x - y)(x + y)

Back-substitute now.

[(2ab - 3(ab + c)][(2ab + 3(ab + c)]

Correct?

Yes, although I would distribute within the factors and then combine like terms. :D
 
  • #5
I thought about distributing within the factors and combining like terms but the question is asking to factor not to simplify after factoring.
 
  • #6
RTCNTC said:
I thought about distributing within the factors and combining like terms but the question is asking to factor not to simplify after factoring.

Well, technically, further simplification is not required to complete the goal of factorization...you have indeed factored...but in my opinion, it's just good practice to simplify whenever possible.
 
  • #7
MarkFL said:
Well, technically, further simplification is not required to complete the goal of factorization...you have indeed factored...but in my opinion, it's just good practice to simplify whenever possible.

I agree.
 

Related to Is it necessary to expand the quantity before factoring the expression?

1. What does it mean to "factor" an expression?

Factoring an expression means to find the numbers or variables that can be multiplied together to get the original expression.

2. Why is factoring important in math and science?

Factoring is important because it simplifies complex expressions, making them easier to work with and manipulate in mathematical and scientific calculations.

3. How do you factor an expression?

To factor an expression, you need to find common factors, use the distributive property, and apply any relevant factoring techniques such as the difference of squares or grouping.

4. What is the difference between factoring and expanding an expression?

Factoring involves breaking down an expression into its simpler components, while expanding involves multiplying out an expression to its expanded form.

5. Can every expression be factored?

No, not every expression can be factored. Some expressions may not have any common factors or may not be able to be simplified using any known factoring techniques.

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