Bunuel
Official Solution:
If \(p\) is a prime number, is \(32p^3 - 16p^2 + 8p - 4\) divisible by \(p^2\)?
Since the first two terms of \(32p^3 - 16p^2 + 8p - 4\) are divisible by \(p^2\), we need to determine if \(8p-4\) is divisible by \(p^2\).
(1) \(p^2 < 25\).
Since \(p\) is a prime number, it can be either \(p=2\) or \(p=3\). If \(p=2\), then \(8p-4\) is divisible by \(p^2=4\). However, if \(p=3\), then \(8p-4\) is NOT divisible by \(p^2=9\). Not sufficient.
(2) \(p^2-8p+12=0\).
Solving this equation, we find that \(p=2\) (the solution \(p=6\) is not valid since 6 is not a prime number). In the case of \(p=2\), we know that \(8p-4\) is divisible by \(p^2=4\). Sufficient.
Answer: B
Thank you for this amazing explaination Bunuel!
I have one question regarding Statement 2): We are looking for two integers whose product is +12 and whose difference is -8. Factoring the quatratic equation I get (p-2) (p-6). As prime numbers are positive, I thought Statement 2) was unsufficient / not possible.
Why should we conver the solution -2 to a +2?
Thank you in advance! Warmest regards
You have correctly factored \(p^2-8p+12=0\) into \((p-2) (p-6)=0\). However, \((p-2) (p-6)=0\) means that p = 2 or p = 6. Not sure how are you got p = -2 there.