Precalculus Examples

$e^{2 x} - 5 e^{x} + 6$

Step 1

Set $e^{2 x} - 5 e^{x} + 6$ equal to $0$ .

$e^{2 x} - 5 e^{x} + 6 = 0$

Step 2

Solve for $x$ .

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Step 2.1

Factor the left side of the equation.

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Step 2.1.1

Rewrite $e^{2 x}$ as ${(e^{x})}^{2}$ .

${(e^{x})}^{2} - 5 e^{x} + 6 = 0$

Step 2.1.2

Let $u = e^{x}$ . Substitute $u$ for all occurrences of $e^{x}$ .

$u^{2} - 5 u + 6 = 0$

Step 2.1.3

Factor $u^{2} - 5 u + 6$ using the AC method.

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Step 2.1.3.1

Consider the form $x^{2} + b x + c$ . Find a pair of integers whose product is $c$ and whose sum is $b$ . In this case, whose product is $6$ and whose sum is $- 5$ .

$- 3, - 2$

Step 2.1.3.2

Write the factored form using these integers.

$(u - 3) (u - 2) = 0$

Step 2.1.4

Replace all occurrences of $u$ with $e^{x}$ .

$(e^{x} - 3) (e^{x} - 2) = 0$

Step 2.2

If any individual factor on the left side of the equation is equal to $0$ , the entire expression will be equal to $0$ .

$e^{x} - 3 = 0$

$e^{x} - 2 = 0$

Step 2.3

Set $e^{x} - 3$ equal to $0$ and solve for $x$ .

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Step 2.3.1

Set $e^{x} - 3$ equal to $0$ .

$e^{x} - 3 = 0$

Step 2.3.2

Solve $e^{x} - 3 = 0$ for $x$ .

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Step 2.3.2.1

Add $3$ to both sides of the equation.

$e^{x} = 3$

Step 2.3.2.2

Take the natural logarithm of both sides of the equation to remove the variable from the exponent.

$\ln (e^{x}) = \ln (3)$

Step 2.3.2.3

Expand the left side.

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Step 2.3.2.3.1

Expand $\ln (e^{x})$ by moving $x$ outside the logarithm.

$x \ln (e) = \ln (3)$

Step 2.3.2.3.2

The natural logarithm of $e$ is $1$ .

$x \cdot 1 = \ln (3)$

Step 2.3.2.3.3

Multiply $x$ by $1$ .

$x = \ln (3)$

Step 2.4

Set $e^{x} - 2$ equal to $0$ and solve for $x$ .

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Step 2.4.1

Set $e^{x} - 2$ equal to $0$ .

$e^{x} - 2 = 0$

Step 2.4.2

Solve $e^{x} - 2 = 0$ for $x$ .

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Step 2.4.2.1

Add $2$ to both sides of the equation.

$e^{x} = 2$

Step 2.4.2.2

Take the natural logarithm of both sides of the equation to remove the variable from the exponent.

$\ln (e^{x}) = \ln (2)$

Step 2.4.2.3

Expand the left side.

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Step 2.4.2.3.1

Expand $\ln (e^{x})$ by moving $x$ outside the logarithm.

$x \ln (e) = \ln (2)$

Step 2.4.2.3.2

The natural logarithm of $e$ is $1$ .

$x \cdot 1 = \ln (2)$

Step 2.4.2.3.3

Multiply $x$ by $1$ .

$x = \ln (2)$

Step 2.5

The final solution is all the values that make $(e^{x} - 3) (e^{x} - 2) = 0$ true.

$x = \ln (3), \ln (2)$

Step 3