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Hi,
Here are some examples of problems like yours before we get to your problem.
Suppose you had 4x² - 81
This is the difference of perfect squares. 4x² is really (2x) squared. 81 is 9². So both factors start with 2x and both end with 9. One binomial has a "-" and the other has a "+".
The factors are (2x - 9)(2x + 9).
Suppose you had 16a² - 49
This is the difference of perfect squares. 16a² is really (4a) squared. 49 is 7². So both factors start with 4a and both end with 7. One binomial has a "-" and the other has a "+". The order does not matter.
The factors are (4a + 7)(4a - 7).
Suppose you had 18x² - 50
18 and 50 are not perfect squares because no number times itself equals either 18 or 50. The problem is that we did not look first for a GCF! This time both terms are divisible by 2. If we divide that out first, we get:
2(9x² - 25) Now we have a difference of perfect squares!
Keep the GCF of 2 out front. The parentheses has a difference of perfect squares. 9x² is really (3x) squared. 25 is 5². So both factors start with 3x and both end with 5. One binomial has a "-" and the other has a "+".
The factors are 2(3x - 5)(3x + 5).
Suppose you had 16x^4 - 81
This is the difference of perfect squares. 16x^4 is really (4x²) squared. 81 is 9². So both factors start with 4x² and both end with 9. One binomial has a "-" and the other has a "+". The order does not matter.
(4x² + 9)(4x² - 9) This is correct so far, but it is not done this time. Notice that with x² in terms with 4 and 9, that they are perfect squares again, so the factor that is the DIFFERENCE of perfect squares can factor again. (The sum of perfect squares can not factor.) So (4x² - 9) factors again into:
(4x² + 9)(4x² - 9)
(4x² + 9)(2x - 3)(2x + 3) <== This is the answer in factored form.
Now, your problem, 16b² - 144
While 16b² - 144 could factor into (4b - 12)(4b + 12), that is not completely factored because the GCF was not divided out first. Instead, divide out a GCF of 16 first.
16b² - 144 =
16(b² - 9) =
Keep the GCF of 16 out front. The parentheses has a difference of perfect squares. b² is really (b) squared. 9 is 3². So both factors start with b and both end with 3. One binomial has a "-" and the other has a "+".
16(b - 3)(b + 3) <==ANSWER
I hope that helps!! :-)