Which statement describes the behavior of the function f(x)=3x/4-x?

AThe graph approaches –3 as x approaches infinity.
BThe graph approaches 0 as x approaches infinity.
CThe graph approaches 3 as x approaches infinity.
DThe graph approaches 4 as x approaches infinity.

Verified Answer :

AThe graph approaches –3 as x approaches infinity.

\(f(x) = \frac{3x}{4-x} +3 -3 = \frac{3x+12-3x}{4-x} -3 = \frac{12}{4-x} -3\)

Answer:

The  graph approaches –3 as x approaches infinity. Option a is correct.

Step-by-step explanation:

The given function is

\(f(x)=\frac{3x}{4-x}\)

We have to find value of function as x approaches infinity. Take limit both sides as x approaches to infinity.

\(\lim_{x\rightarrow \infty}f(x)=\lim_{x\rightarrow \infty}\frac{3x}{4-x}\)

Taking x common from the denominator.

\(\lim_{x\rightarrow \infty}f(x)=\lim_{x\rightarrow \infty}\frac{3x}{x(\frac{4}{x}-1)}\)

Cancel out common factor x.

\(\lim_{x\rightarrow \infty}f(x)=\lim_{x\rightarrow \infty}\frac{3}{\frac{4}{x}-1}\)

Apply limits.

\(\lim_{x\rightarrow \infty}f(x)=\frac{3}{\frac{4}{\infty}-1}\)

\(\lim_{x\rightarrow \infty}f(x)=\frac{3}{0-1}\)

\(\lim_{x\rightarrow \infty}f(x)=-3\)

Therefore the  graph approaches –3 as x approaches infinity.

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