Prove: If m is an even integer, then (5m + 4) is an even integer. We see that 5m + 4 = 10n + 4 = 2(5n + 2). Therefore, (5m + 4) is an even integer.
For the following proofs:
• If the proposition is false, then the proposed proof is incorrect. In this case, either find the
error in the proof or provide a counterexample showing that the proposition is false.
• If the proposition is true, the proposed proof may still be wrong. In this case, identify the
error and provide a correct proof.
• If the proposition is true and the proposed proof is incomplete, then indicate how the proof
could be improved by rewriting it.
A) Prove: If m is an even integer, then (5m + 4) is an even integer.
We see that 5m + 4 = 10n + 4 = 2(5n + 2). Therefore, (5m + 4) is an even integer.
B) The notation a—b indicates that a divides b, that is that the result of b/a is an
integer. Prove: For all integers a, b, and c, if a|(bc), then a|b or a|c.
We assume that a, b, and c are integers and that a divides bc. So, there exists an integer
k such that bc = ka. We now factor k as k = mn, where m and n are integers. We then
see that
bc = mna.
This means that b = ma or c = na and hence, a|b or a|c
C) Prove: For all integers m and n, if mn is an even integer, then m is even or n is
even.
For either m or n to be even, there exists an integer k such that m = 2k or n = 2k. So
if we multiply m and n, the product will contain a factor of 2 and, hence, mn will be
even
![2.
For the following proofs:
• If the proposition is false, then the proposed proof is incorrect. In this case, either find the
error in the proof or provide a counterexample showing that the proposition is false.
• If the proposition is true, the proposed proof may still be wrong. In this case, identify the
error and provide a correct proof.
• If the proposition is true and the proposed proof is incomplete, then indicate how the proof
could be improved by rewriting it.
(a)
Prove: If m is an even integer, then (5m + 4) is an even integer.
Proof.
We see that 5m + 4 = 10n +4=2(5n+2). Therefore, (5m + 4) is an even integer. D
(c)
Solution:
(b)
The notation ab indicates that a divides b, that is that the result of
integer. Prove: For all integers a, b, and c, if al(bc), then alb or alc.
Proof.
We assume that a, b, and c are integers and that a divides bc. So, there exists an integer
k such that be = ka. We now factor k as k = mn, where m and n are integers. We then
see that
bc=mna.
This means that b=ma or c=na and hence, alb or alc.
Is an
Solution:
Prove: For all integers m and n, if mn is an even integer, then m is even or 72 is
even.
Proof.
For either m or n to be even, there exists an integer k such that m = 2k or n = 2k. So
if we multiply m and n, the product will contain a factor of 2 and, hence, mn will be
even.](/v2/_next/image?url=https%3A%2F%2Fcontent.bartleby.com%2Fqna-images%2Fquestion%2Fb85b6a62-8f66-4255-b64b-cdb85a3186b3%2F0352ec50-e492-4554-a144-fed23ed96252%2Fi4w94wa_processed.jpeg&w=3840&q=75)
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