Calculus Examples

$lim_{x \to π} \frac{\sin (3 x)}{π - x}$

Step 1

Apply L'Hospital's rule.

Tap for more steps...

Step 1.1

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

Tap for more steps...

Step 1.1.1

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

$\frac{lim_{x \to π} \sin (3 x)}{lim_{x \to π} π - x}$

Step 1.1.2

Evaluate the limit of the numerator.

Tap for more steps...

Step 1.1.2.1

Evaluate the limit.

Tap for more steps...

Step 1.1.2.1.1

Move the limit inside the trig function because sine is continuous.

$\frac{\sin (lim_{x \to π} 3 x)}{lim_{x \to π} π - x}$

Step 1.1.2.1.2

Move the term $3$ outside of the limit because it is constant with respect to $x$ .

$\frac{\sin (3 lim_{x \to π} x)}{lim_{x \to π} π - x}$

Step 1.1.2.2

Evaluate the limit of $x$ by plugging in $π$ for $x$ .

$\frac{\sin (3 π)}{lim_{x \to π} π - x}$

Step 1.1.2.3

Simplify the answer.

Tap for more steps...

Step 1.1.2.3.1

Subtract full rotations of $2 π$ until the angle is greater than or equal to $0$ and less than $2 π$ .

$\frac{\sin (π)}{lim_{x \to π} π - x}$

Step 1.1.2.3.2

Apply the reference angle by finding the angle with equivalent trig values in the first quadrant.

$\frac{\sin (0)}{lim_{x \to π} π - x}$

Step 1.1.2.3.3

The exact value of $\sin (0)$ is $0$ .

$\frac{0}{lim_{x \to π} π - x}$

Step 1.1.3

Evaluate the limit of the denominator.

Tap for more steps...

Step 1.1.3.1

Evaluate the limit.

Tap for more steps...

Step 1.1.3.1.1

Split the limit using the Sum of Limits Rule on the limit as $x$ approaches $π$ .

$\frac{0}{lim_{x \to π} π - lim_{x \to π} x}$

Step 1.1.3.1.2

Evaluate the limit of $π$ which is constant as $x$ approaches $π$ .

$\frac{0}{π - lim_{x \to π} x}$

Step 1.1.3.2

Evaluate the limit of $x$ by plugging in $π$ for $x$ .

$\frac{0}{π - π}$

Step 1.1.3.3

Subtract $π$ from $π$ .

$\frac{0}{0}$

Step 1.1.3.4

The expression contains a division by $0$ . The expression is undefined.

Undefined

$\frac{0}{0}$

Step 1.1.4

The expression contains a division by $0$ . The expression is undefined.

Undefined

$\frac{0}{0}$

Step 1.2

Since $\frac{0}{0}$ 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.

$lim_{x \to π} \frac{\sin (3 x)}{π - x} = lim_{x \to π} \frac{\frac{d}{d x} [\sin (3 x)]}{\frac{d}{d x} [π - x]}$

Step 1.3

Find the derivative of the numerator and denominator.

Tap for more steps...

Step 1.3.1

Differentiate the numerator and denominator.

$lim_{x \to π} \frac{\frac{d}{d x} [\sin (3 x)]}{\frac{d}{d x} [π - x]}$

Step 1.3.2

Differentiate using the chain rule, which states that $\frac{d}{d x} [f (g (x))]$ is $f' (g (x)) g' (x)$ where $f (x) = \sin (x)$ and $g (x) = 3 x$ .

Tap for more steps...

Step 1.3.2.1

To apply the Chain Rule, set $u$ as $3 x$ .

$lim_{x \to π} \frac{\frac{d}{d u} [\sin (u)] \frac{d}{d x} [3 x]}{\frac{d}{d x} [π - x]}$

Step 1.3.2.2

The derivative of $\sin (u)$ with respect to $u$ is $\cos (u)$ .

$lim_{x \to π} \frac{\cos (u) \frac{d}{d x} [3 x]}{\frac{d}{d x} [π - x]}$

Step 1.3.2.3

Replace all occurrences of $u$ with $3 x$ .

$lim_{x \to π} \frac{\cos (3 x) \frac{d}{d x} [3 x]}{\frac{d}{d x} [π - x]}$

Step 1.3.3

Since $3$ is constant with respect to $x$ , the derivative of $3 x$ with respect to $x$ is $3 \frac{d}{d x} [x]$ .

$lim_{x \to π} \frac{\cos (3 x) (3 \frac{d}{d x} [x])}{\frac{d}{d x} [π - x]}$

Step 1.3.4

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

$lim_{x \to π} \frac{\cos (3 x) (3 \cdot 1)}{\frac{d}{d x} [π - x]}$

Step 1.3.5

Multiply $3$ by $1$ .

$lim_{x \to π} \frac{\cos (3 x) \cdot 3}{\frac{d}{d x} [π - x]}$

Step 1.3.6

Move $3$ to the left of $\cos (3 x)$ .

$lim_{x \to π} \frac{3 \cdot \cos (3 x)}{\frac{d}{d x} [π - x]}$

Step 1.3.7

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

$lim_{x \to π} \frac{3 \cos (3 x)}{\frac{d}{d x} [π] + \frac{d}{d x} [- x]}$

Step 1.3.8

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

$lim_{x \to π} \frac{3 \cos (3 x)}{0 + \frac{d}{d x} [- x]}$

Step 1.3.9

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

Tap for more steps...

Step 1.3.9.1

Since $- 1$ is constant with respect to $x$ , the derivative of $- x$ with respect to $x$ is $- \frac{d}{d x} [x]$ .

$lim_{x \to π} \frac{3 \cos (3 x)}{0 - \frac{d}{d x} [x]}$

Step 1.3.9.2

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

$lim_{x \to π} \frac{3 \cos (3 x)}{0 - 1 \cdot 1}$

Step 1.3.9.3

Multiply $- 1$ by $1$ .

$lim_{x \to π} \frac{3 \cos (3 x)}{0 - 1}$

Step 1.3.10

Subtract $1$ from $0$ .

$lim_{x \to π} \frac{3 \cos (3 x)}{- 1}$

Step 1.4

Move the negative one from the denominator of $\frac{3 \cos (3 x)}{- 1}$ .

$lim_{x \to π} - 1 \cdot (3 \cos (3 x))$

Step 2

Evaluate the limit.

Tap for more steps...

Step 2.1

Move the term $- 1 \cdot 3$ outside of the limit because it is constant with respect to $x$ .

$- 1 \cdot 3 lim_{x \to π} \cos (3 x)$

Step 2.2

Move the limit inside the trig function because cosine is continuous.

$- 3 \cos (lim_{x \to π} 3 x)$

Step 2.3

Move the term $3$ outside of the limit because it is constant with respect to $x$ .

$- 3 \cos (3 lim_{x \to π} x)$

Step 3

Evaluate the limit of $x$ by plugging in $π$ for $x$ .

$- 3 \cos (3 π)$

Step 4

Simplify the answer.

Tap for more steps...

Step 4.1

Subtract full rotations of $2 π$ until the angle is greater than or equal to $0$ and less than $2 π$ .

$- 3 \cos (π)$

Step 4.2

Apply the reference angle by finding the angle with equivalent trig values in the first quadrant. Make the expression negative because cosine is negative in the second quadrant.

$- 3 (- \cos (0))$

Step 4.3

The exact value of $\cos (0)$ is $1$ .

$- 3 (- 1 \cdot 1)$

Step 4.4

Multiply $- 3 (- 1 \cdot 1)$ .

Tap for more steps...

Step 4.4.1

Multiply $- 1$ by $1$ .

$- 3 \cdot - 1$

Step 4.4.2

Multiply $- 3$ by $- 1$ .

$3$