ACT Math : Graphing

Study concepts, example questions & explanations for ACT Math

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Example Questions

Example Question #12 : How To Graph An Exponential Function

If the functions 

\(\displaystyle f(x) = e^{x}+ 9\)

\(\displaystyle g(x) = 4e^{x}- 7\)

were graphed on the same coordinate axes, what would be the \(\displaystyle x\)-coordinate of their point of intersection?

Round to the nearest tenth, if applicable.

Possible Answers:

The graphs of \(\displaystyle f\) and \(\displaystyle g\) would not intersect.

\(\displaystyle 2.7\)

\(\displaystyle 5.3\)

\(\displaystyle 14.3\)

\(\displaystyle 1.7\)

Correct answer:

\(\displaystyle 1.7\)

Explanation:

We can rewrite the statements using \(\displaystyle y\) for both \(\displaystyle f(x)\) and \(\displaystyle g(x)\) as follows:

\(\displaystyle y = e^{x}+ 9\)

\(\displaystyle y = 4e^{x}- 7\)

To solve this, we can set the expressions equal, as follows:

\(\displaystyle 4e^{x}- 7 = e^{x}+ 9\)

\(\displaystyle 4e^{x}- 7 - e^{x} + 7 = e^{x}+ 9 - e^{x} + 7\)

\(\displaystyle 3e^{x} = 16\)

\(\displaystyle 3e^{x}\div 3 = 16 \div 3\)

\(\displaystyle e^{x} = \approc 5.3333\)

\(\displaystyle x \approx \ln 5.333 \approx 1.7\)

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