Determine if a Relation is a Function - Pre-Calculus

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Question

Which of the following expressions is not a function?

Answer

Recall that an expression is only a function if it passes the vertical line test. Test this by graphing each function and looking for one which fails the vertical line test. (The vertical line test consists of drawing a vertical line through the graph of an expression. If the vertical line crosses the graph of the expression more than once, the expression is not a function.)

Functions can only have one y value for every x value. The only choice that reflects this is:

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Question

Suppose we have the relation on the set of real numbers whenever . Which of the following is true.

Answer

The relation is not a function because and hold. If it were a function, would hold only for one . But we know it holds for because and . Thus, the relation on the set of real numbers is not a function.

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Question

Consider a family consisting of a two parents, Juan and Oksana, and their daughters Adriana and Laksmi. A relation is true whenever is the child of . Which of the following is not true?

Answer

The statement

"Even if the two parents had only one daughter, the relation would not be a function."

is not true because if they had only one daughter, say Adriana, then the only relations that would exist would be (Juan, Adriana) and (Oksana,Adriana), which defines a function.

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Question

Which of the following relations is not a function?

Answer

The definition of a function requires that for each input (i.e. each value of ), there is only one output (i.e. one value of ). For , each value of corresponds to two values of (for example, when , both and are correct solutions). Therefore, this relation cannot be a function.

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Question

Given the set of ordered pairs, determine if the relation is a function

Answer

A relation is a function if no single x-value corresponds to more than one y-value.

Because the mapping from goes to and

the relation is NOT a function.

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Question

What equation is perpendicular to and passes throgh ?

Answer

First find the reciprocal of the slope of the given function.

The perpendicular function is:

Now we must find the constant, , by using the given point that the perpendicular crosses.

solve for :

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Question

Is the following relation of ordered pairs a function?

Answer

A set of ordered pairs is a function if it passes the vertical line test.

Because there are no more than one corresponding value for any given value, the relation of ordered pairs IS a function.

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