Math 240
Proof Evaluation #1 M. Flashman
Let A={ x in R
: x2 + 1 < 10} and B= { x in R : 0 < x < 2}
Proposition 1: B is a subset of A.
Proof: By the definition of subset, we need to
show that if r is an element of B then r is an element of
A. Suppose r is an element of B. Then 0 < r < 2, and
thus
0 < r2 < 4 so that 0 <
r2 +1 < 5. So it should be clear that r is an
element of A. EOP.
Proposition 2: A is not a subset of B.
Proof: Consider the number -1, which is a member
of A, but is not a member of B. Thus it is not the case that every member
of A is a member of B. EOP.
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Are the statements in propositions 1 and 2 conditional
or
absolute? [Note: For the purpose of this analysis a conditional
statement is a statement that is expressed in the form; "If p then q",
or "p implies q". An absolute statement is a statement that is not conditional.]
-
List the variables used in these propositions. Indicate what
these variables represent.
- Does the proof (for Proposition 1 and 2) proceed forward
or is it mixed with some backward argument? If it has some backward argument,
indicate briefly how the original conclusion is altered.
-
Did the proofs explicitly leave some steps for the
reader to complete? If so, state what steps the reader is expected to complete.
[Optional: complete these steps.]
-
Did the proofs implicitly leave some steps for the
reader to complete? If so, state what steps you think the reader is expected
to complete. [Optional: complete these steps.]
-
Indicate any parts of the arguments that you felt needed greater
detail or better connection to the proofs. [Optional: Supply these details
or suggest a better connection.]
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Overall, do you think these proofs were effective? Discuss
briefly the basis for you conclusion.