Precalculus Examples

$3^{2 x} + 3^{x + 1} - 4 = 0$

Step 1

Factor the left side of the equation.

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Step 1.1

Rewrite $3^{x + 1}$ as $3^{x} \cdot 3^{1}$ .

$3^{2 x} + 3^{x} \cdot 3 - 4 = 0$

Step 1.2

Rewrite $3^{2 x}$ as ${(3^{x})}^{2}$ .

${(3^{x})}^{2} + 3^{x} \cdot 3 - 4 = 0$

Step 1.3

Let $u = 3^{x}$ . Substitute $u$ for all occurrences of $3^{x}$ .

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Step 1.3.1

Evaluate the exponent.

$u^{2} + u \cdot 3 - 4 = 0$

Step 1.3.2

Move $3$ to the left of $u$ .

$u^{2} + 3 u - 4 = 0$

Step 1.4

Factor $u^{2} + 3 u - 4$ using the AC method.

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Step 1.4.1

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 $- 4$ and whose sum is $3$ .

$- 1, 4$

Step 1.4.2

Write the factored form using these integers.

$(u - 1) (u + 4) = 0$

Step 1.5

Replace all occurrences of $u$ with $3^{x}$ .

$(3^{x} - 1) (3^{x} + 4) = 0$

Step 2

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

$3^{x} - 1 = 0$

$3^{x} + 4 = 0$

Step 3

Set $3^{x} - 1$ equal to $0$ and solve for $x$ .

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Step 3.1

Set $3^{x} - 1$ equal to $0$ .

$3^{x} - 1 = 0$

Step 3.2

Solve $3^{x} - 1 = 0$ for $x$ .

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Step 3.2.1

Add $1$ to both sides of the equation.

$3^{x} = 1$

Step 3.2.2

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

$\ln (3^{x}) = \ln (1)$

Step 3.2.3

Expand $\ln (3^{x})$ by moving $x$ outside the logarithm.

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

Step 3.2.4

Simplify the right side.

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Step 3.2.4.1

The natural logarithm of $1$ is $0$ .

$x \ln (3) = 0$

Step 3.2.5

Divide each term in $x \ln (3) = 0$ by $\ln (3)$ and simplify.

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Step 3.2.5.1

Divide each term in $x \ln (3) = 0$ by $\ln (3)$ .

$\frac{x \ln (3)}{\ln (3)} = \frac{0}{\ln (3)}$

Step 3.2.5.2

Simplify the left side.

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Step 3.2.5.2.1

Cancel the common factor of $\ln (3)$ .

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Step 3.2.5.2.1.1

Cancel the common factor.

$\frac{x \ln (3)}{\ln (3)} = \frac{0}{\ln (3)}$

Step 3.2.5.2.1.2

Divide $x$ by $1$ .

$x = \frac{0}{\ln (3)}$

Step 3.2.5.3

Simplify the right side.

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Step 3.2.5.3.1

Divide $0$ by $\ln (3)$ .

$x = 0$

Step 4

Set $3^{x} + 4$ equal to $0$ and solve for $x$ .

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Step 4.1

Set $3^{x} + 4$ equal to $0$ .

$3^{x} + 4 = 0$

Step 4.2

Solve $3^{x} + 4 = 0$ for $x$ .

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Step 4.2.1

Subtract $4$ from both sides of the equation.

$3^{x} = - 4$

Step 4.2.2

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

$\ln (3^{x}) = \ln (- 4)$

Step 4.2.3

The equation cannot be solved because $\ln (- 4)$ is undefined.

Undefined

Step 4.2.4

There is no solution for $3^{x} = - 4$

No solution

Step 5

The final solution is all the values that make $(3^{x} - 1) (3^{x} + 4) = 0$ true.

$x = 0$