Calculus Examples

$lim_{x \to \infty} \frac{e^{x}}{5 x + 200}$

Step 1

Evaluate the limit of the numerator and the limit of the denominator.

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Step 1.1

Take the limit of the numerator and the limit of the denominator.

$\frac{lim_{x \to \infty} e^{x}}{lim_{x \to \infty} 5 x + 200}$

Step 1.2

Since the exponent $x$ approaches $\infty$ , the quantity $e^{x}$ approaches $\infty$ .

$\frac{\infty}{lim_{x \to \infty} 5 x + 200}$

Step 1.3

The limit at infinity of a polynomial whose leading coefficient is positive is infinity.

$\frac{\infty}{\infty}$

Step 1.4

Infinity divided by infinity is undefined.

Undefined

$\frac{\infty}{\infty}$

Step 2

Since $\frac{\infty}{\infty}$ is of indeterminate form, apply L'Hospital's Rule. L'Hospital's Rule states that the limit of a quotient of functions is equal to the limit of the quotient of their derivatives.

$lim_{x \to \infty} \frac{e^{x}}{5 x + 200} = lim_{x \to \infty} \frac{\frac{d}{d x} [e^{x}]}{\frac{d}{d x} [5 x + 200]}$

Step 3

Find the derivative of the numerator and denominator.

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Step 3.1

Differentiate the numerator and denominator.

$lim_{x \to \infty} \frac{\frac{d}{d x} [e^{x}]}{\frac{d}{d x} [5 x + 200]}$

Step 3.2

Differentiate using the Exponential Rule which states that $\frac{d}{d x} [a^{x}]$ is $a^{x} \ln (a)$ where $a$ = $e$ .

$lim_{x \to \infty} \frac{e^{x}}{\frac{d}{d x} [5 x + 200]}$

Step 3.3

By the Sum Rule, the derivative of $5 x + 200$ with respect to $x$ is $\frac{d}{d x} [5 x] + \frac{d}{d x} [200]$ .

$lim_{x \to \infty} \frac{e^{x}}{\frac{d}{d x} [5 x] + \frac{d}{d x} [200]}$

Step 3.4

Evaluate $\frac{d}{d x} [5 x]$ .

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Step 3.4.1

Since $5$ is constant with respect to $x$ , the derivative of $5 x$ with respect to $x$ is $5 \frac{d}{d x} [x]$ .

$lim_{x \to \infty} \frac{e^{x}}{5 \frac{d}{d x} [x] + \frac{d}{d x} [200]}$

Step 3.4.2

Differentiate using the Power Rule which states that $\frac{d}{d x} [x^{n}]$ is $n x^{n - 1}$ where $n = 1$ .

$lim_{x \to \infty} \frac{e^{x}}{5 \cdot 1 + \frac{d}{d x} [200]}$

Step 3.4.3

Multiply $5$ by $1$ .

$lim_{x \to \infty} \frac{e^{x}}{5 + \frac{d}{d x} [200]}$

Step 3.5

Since $200$ is constant with respect to $x$ , the derivative of $200$ with respect to $x$ is $0$ .

$lim_{x \to \infty} \frac{e^{x}}{5 + 0}$

Step 3.6

Add $5$ and $0$ .

$lim_{x \to \infty} \frac{e^{x}}{5}$

Step 4

Since the function $e^{x}$ approaches $\infty$ , the positive constant $\frac{1}{5}$ times the function also approaches $\infty$ .

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Step 4.1

Consider the limit with the constant multiple $\frac{1}{5}$ removed.

$lim_{x \to \infty} e^{x}$

Step 4.2

Since the exponent $x$ approaches $\infty$ , the quantity $e^{x}$ approaches $\infty$ .

$\infty$