Consider the following theorem. Theorem: For all sets A and B, if A C B, then A U B CB. Supply explanations for the steps in the proof of the theorem. Proof: Statement Explanation Suppose A, B, and C are any sets such that AC B. starting point We must show that A UBC B. conclusion to be shown Let x be any element in AU B. start of an element proof Then x is in A or x is in B. ---Select--- In case x is in A, then x is in B ---Select--- In case x is in B, then x is in B. tautology (p → P). So in either case, x is in B. proof by division into cases Thus every element in A UB is in B. since x could be any element of A U B Therefore, A UBCB --Select--- [as was to be shown].

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Consider the following theorem.
Theorem: For all sets A and B, if A C B, then A U B CB.
Supply explanations for the steps in the proof of the theorem.
Proof:
Statement
Explanation
Suppose A, B, and C are any sets such that A C B.
starting point
We must show that A UBC B.
conclusion to be shown
Let x be any element in AU B.
start of an element proof
Then x is in A or x is in B.
---Select---
In case x is in A, then x is in B
-Select---
In case x is in B, then x is in B.
tautology (p → p)
So in either case, x is in B.
proof by division into cases
Thus every element in A UB is in B.
since x could be any element of A U B
---Select---
Therefore, AUBC B
[as was to be shown].
Transcribed Image Text:Consider the following theorem. Theorem: For all sets A and B, if A C B, then A U B CB. Supply explanations for the steps in the proof of the theorem. Proof: Statement Explanation Suppose A, B, and C are any sets such that A C B. starting point We must show that A UBC B. conclusion to be shown Let x be any element in AU B. start of an element proof Then x is in A or x is in B. ---Select--- In case x is in A, then x is in B -Select--- In case x is in B, then x is in B. tautology (p → p) So in either case, x is in B. proof by division into cases Thus every element in A UB is in B. since x could be any element of A U B ---Select--- Therefore, AUBC B [as was to be shown].
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