# GMAT Math : DSQ: Understanding functions

## Example Questions

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### Example Question #61 : Dsq: Understanding Functions

Given a function , it is known that:

Given a function , evaluate .

Statement 1:  is an odd function.

Statement 2:  for every positive integer .

Statement 2 ALONE is sufficient to answer the question, but Statement 1 ALONE is NOT sufficient to answer the question.

Statement 1 ALONE is sufficient to answer the question, but Statement 2 ALONE is NOT sufficient to answer the question.

BOTH statements TOGETHER are sufficient to answer the question, but NEITHER statement ALONE is sufficient to answer the question.

BOTH statements TOGETHER are insufficient to answer the question.

EITHER statement ALONE is sufficient to answer the question.

Statement 1 ALONE is sufficient to answer the question, but Statement 2 ALONE is NOT sufficient to answer the question.

Explanation:

, so to answer the question, it is necessary and sufficient to evaluate .

Assume Statement 1 alone. By defintion of an odd function, from Statement 2, for every  in the domain of . In specific, setting

.

The only number whose opposite is itself is 0, so

and it follows that

.

Statement 2 only gives the values of  for positive integers; this information is irrelevant.

### Example Question #3001 : Gmat Quantitative Reasoning

Let be a function with the set of all real numbers as its domain, and let the function have an inverse .

What is the -intercept of the graph of  ?

Statement 1: .

Statement 2: The graphs of and intersect only at the point .

EITHER STATEMENT ALONE provides sufficient information to answer the question.

BOTH STATEMENTS TOGETHER provide sufficient information to answer the question, but NEITHER STATEMENT ALONE provides sufficient information to answer the question.

BOTH STATEMENTS TOGETHER do NOT provide sufficient information to answer the question.

STATEMENT 1 ALONE provides sufficient information to answer the question, but STATEMENT 2 ALONE does NOT provide sufficient information to answer the question.

STATEMENT 2 ALONE provides sufficient information to answer the question, but STATEMENT 1 ALONE does NOT provide sufficient information to answer the question.

BOTH STATEMENTS TOGETHER do NOT provide sufficient information to answer the question.

Explanation:

The -intercept of the graph of is the point at which the graph intersects the -axis. At that point, , or, equivalently, .

Therefore, we need to find the value for which

Between the two statements, we only know that  and . The value of  for which  cannot be determined.

### Example Question #61 : Dsq: Understanding Functions

True or false:  is an arithmetic sequence.

Statement 1:

Statement 2:

BOTH STATEMENTS TOGETHER do NOT provide sufficient information to answer the question.

EITHER STATEMENT ALONE provides sufficient information to answer the question.

STATEMENT 2 ALONE provides sufficient information to answer the question, but STATEMENT 1 ALONE does NOT provide sufficient information to answer the question.

STATEMENT 1 ALONE provides sufficient information to answer the question, but STATEMENT 2 ALONE does NOT provide sufficient information to answer the question.

BOTH STATEMENTS TOGETHER provide sufficient information to answer the question, but NEITHER STATEMENT ALONE provides sufficient information to answer the question.

STATEMENT 1 ALONE provides sufficient information to answer the question, but STATEMENT 2 ALONE does NOT provide sufficient information to answer the question.

Explanation:

An arithmetic sequence is one in which the difference of each term in the sequence and the one preceding is constant.

Assume Statement 1 alone.

,

meaning that at least two such differences are unequal, and proving the sequence is not arithmetic.

Statement 2 alone only proves that two such differences are equal, but says nothing about any of the other (infinitely many) such differences. Therefore, it leaves the question unresolved.

### Example Question #64 : Functions/Series

Define  and

Is it true that  ?

Statement 1:

Statement 2:

EITHER statement ALONE is sufficient to answer the question.

Statement 1 ALONE is sufficient to answer the question, but Statement 2 ALONE is NOT sufficient to answer the question.

BOTH statements TOGETHER are sufficient to answer the question, but NEITHER statement ALONE is sufficient to answer the question.

Statement 2 ALONE is sufficient to answer the question, but Statement 1 ALONE is NOT sufficient to answer the question.

BOTH statements TOGETHER are insufficient to answer the question.

EITHER statement ALONE is sufficient to answer the question.

Explanation:

For  to be each other's inverse, it must be true that

and

We can look at the first condition.

For this to be true, it must hold that:

and

Since both statements violate these conditions, it is impossible for , even if you are only given one of them.

The answer is that either statement alone is sufficient to answer the question.

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