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Which equation has [tex]$x=4$[/tex] as the solution?

A. [tex]\log _4(3 x+4)=2[/tex]
B. [tex]\log _3(2 x-5)=2[/tex]
C. [tex]\log _x 64=4[/tex]
D. [tex]\log _x 16=4[/tex]


Sagot :

Sure, let's determine which of the given equations has [tex]\( x = 4 \)[/tex] as the solution. There are four equations to consider. Let's solve each one step-by-step.

### Equation 1: [tex]\(\log _4(3x+4)=2\)[/tex]

First, we convert the logarithmic equation to its exponential form.

[tex]\[ 4^2 = 3x + 4 \][/tex]

Calculate [tex]\(4^2\)[/tex]:

[tex]\[ 16 = 3x + 4 \][/tex]

Subtract 4 from both sides to isolate the term with [tex]\(x\)[/tex]:

[tex]\[ 16 - 4 = 3x \][/tex]

[tex]\[ 12 = 3x \][/tex]

Divide both sides by 3 to solve for [tex]\(x\)[/tex]:

[tex]\[ x = \frac{12}{3} = 4 \][/tex]

Thus, the solution to the first equation is [tex]\(x = 4\)[/tex].

### Equation 2: [tex]\(\log _3(2x-5)=2\)[/tex]

Convert the logarithmic equation to its exponential form:

[tex]\[ 3^2 = 2x - 5 \][/tex]

Calculate [tex]\(3^2\)[/tex]:

[tex]\[ 9 = 2x - 5 \][/tex]

Add 5 to both sides:

[tex]\[ 9 + 5 = 2x \][/tex]

[tex]\[ 14 = 2x \][/tex]

Divide both sides by 2:

[tex]\[ x = \frac{14}{2} = 7 \][/tex]

The solution to the second equation is [tex]\(x = 7\)[/tex], not 4.

### Equation 3: [tex]\(\log _x 64=4\)[/tex]

Convert the logarithmic equation to its exponential form:

[tex]\[ x^4 = 64 \][/tex]

Take the fourth root of both sides:

[tex]\[ x = \sqrt[4]{64} \][/tex]

Calculate [tex]\(\sqrt[4]{64}: \[ x = 2^{\frac{6}{4}} = 2^{1.5} \neq 4 \] The solution to the third equation is not \(x = 4\)[/tex].

### Equation 4: [tex]\(\log _x 16=4\)[/tex]

Convert the logarithmic equation to its exponential form:

[tex]\[ x^4 = 16 \][/tex]

Take the fourth root of both sides:

[tex]\[ x = \sqrt[4]{16} \][/tex]

Calculate [tex]\(\sqrt[4]{16}\)[/tex]:

[tex]\[ x = 2 \][/tex]

The solution to the fourth equation is [tex]\(x = 2\)[/tex], not 4.

### Conclusion
Among the four equations, only the first equation [tex]\(\log _4(3 x+4)=2\)[/tex] has [tex]\(x = 4\)[/tex] as the solution. Thus, the correct answer is the first equation.