Let and . Then which of the following statements is (are) TRUE?
Correct Answer :
For any given if and only if b = 0, where
Solution :
To determine which of the statements are true, let us analyze each of them step-by-step.
First, recall the definitions of the sets given in the problem statement:
Step 1: Analyze the statement
Let us check if each of the subsets , , and is contained in .
1. For any integer , we can write . Since , we have . Thus, .
2. Note that the set is closed under addition, subtraction, and multiplication because it is the ring of integers of the quadratic field . Specifically, if , then .
Since (with ), any positive integer power must also belong to by mathematical induction. Hence, .
3. Similarly, since (with ), any positive integer power must also belong to . Hence, .
Combining these results, we get . Therefore, this statement is TRUE.
Step 2: Analyze the statement
Let us analyze the base of the exponent in :
Since , we have:
For a base where , the sequence is strictly decreasing and approaches as .
Thus, for a sufficiently large , we can always find .
Therefore, the intersection is not empty. This statement is FALSE.
Step 3: Analyze the statement
Let us analyze the base of the exponent in :
Since , the sequence is strictly increasing and diverges to as .
Thus, we can definitely find a positive integer such that (for instance, ).
Therefore, the intersection is non-empty. This statement is TRUE.
Step 4: Analyze the statement: For any given , if and only if
Using Euler's formula, let:
If , then must be a real number. For to be real, the imaginary part must be zero:
This occurs if and only if the argument is an integer multiple of :
Dividing by :
Rearranging the equation:
Since , the right-hand side is an integer.
If , then , which implies that is rational. This is a contradiction since is irrational.
Thus, we must have .
Conversely, if , then:
Since , .
Hence, if and only if . This statement is TRUE.
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