Question

Which of the following expressions are equivalent to 48a^3-75a? Select all that apply.

Answer 1

Answer:

• Answer 2) 3a(16a^2-25)
• Answer 4) 3a(4a+5)(4a-5)
• Answer 5) -3a(25-16a^2)
• Answer 6) -3a(5-4a)(5+4a)

Step-by-step explanation:

The factors of each term are ...

• 2·2·2·2·3·a·a·a
• 3·5·5·a

So, the greatest common factor is 3a. Factoring that out gives ...

  3a(16a^2 -25) . . . . . . matches answer 2

The factor in parentheses is the difference of squares, so it can be factored. You have memorized the form for the difference of squares ...

  p^2 -q^2 = (p -q)(p +q)

so you know the factoring of this with p=4a and q=5 will be ...

  3a(4a -5)(4a +5) . . . . . . matches answer 4

__

Any pair of factors can be multiplied by -1 without changing the value of the expression. So, two more answers are equivalent:

   (-3a)(-(16a^2 -25) = -3a(25 -16a^2) . . . . . . matches answer 5

  (-3a)(-(4a -5)(4a +5) = -3a(5 -4a)(5 +4a) . . . . . . matches answer 6

Answer 2

Answer:

2 4 5 6

Step-by-step explanation:

The highest common factor is 3a That means that 48a^3 must be divided by 3a which means 48a^3 / 3a = 16a^2. Notice what happened. 48/3 = 16. a^3/a = a^2.

Now you have to pull out 3a from 75a. That wasn't done to Answer 1. So answer one is incorrect.

75a/3a = 25

So far what you answer looks like is

3a(16a^2 - 25) which is answer 2

===========================================

Answer 3 is wrong because one of the factor has to be - 5. Neither one is.

===========================================

Answer 4 is correct

16a^2 - 25 factors into (4a - 5)(4a + 5)

So what is written reflects those factors + the 3a

==============================================

Now we come to the brutal ones.

If you take out a minus sign from the brackets, it has the effect of turning the two terms inside the brackets around.

-3a(25 - 16a^2) is what the above sentence means. so 5 is correct

==============================================

The two terms inside the brackets still factor

-3a ( 5 - 4a)(5 + 4a) It is just that they are turned around.

6 is correct.

===============================================