Solve Complex Logarithmic Equation: 1/(log_x3) × x²log_(1/x)27 + 4x + 6 = 0

Question

1logx3×x2log1x27+4x+6=0 \frac{1}{\log_x3}\times x^2\log_{\frac{1}{x}}27+4x+6=0

x=? x=\text{?}

Video Solution

Solution Steps

00:00 Solve
00:06 Use the formula for reciprocal logarithm, we'll get the inverse logarithm
00:16 Use the logarithm product formula, switch between the bases
00:31 Solve the logarithm and substitute in the exercise
00:41 1 divided by the number equals the number to the power of -1
00:51 Solve the logarithm and substitute in the exercise
01:16 Collect terms and arrange the equation
01:21 Use the root formula to find possible solutions
01:31 Calculate and solve
01:41 There are 2 solutions, addition and subtraction
02:01 Check the domain of definition
02:07 And this is the solution to the question

Step-by-Step Solution

To solve the given equation, we need to simplify the logarithmic expressions and then solve for x x . Let's proceed with the given equation:

1logx3×x2log1/x27+4x+6=0\frac{1}{\log_x 3} \times x^2 \log_{1/x} 27 + 4x + 6 = 0

Step 1: Simplify the logarithmic terms.

Apply the change of base formula to the logarithms:

logx3=ln3lnx\log_x 3 = \frac{\ln 3}{\ln x}

Thus, 1logx3=lnxln3\frac{1}{\log_x 3} = \frac{\ln x}{\ln 3}.

For the second logarithmic term: log1/x27=logx27=ln27lnx\log_{1/x} 27 = -\log_x 27 = -\frac{\ln 27}{\ln x}.

Step 2: Substitute these simplifications back into the equation.

We have:

lnxln3×x2×ln27lnx+4x+6=0\frac{\ln x}{\ln 3} \times x^2 \times -\frac{\ln 27}{\ln x} + 4x + 6 = 0

Simplify this expression:

The lnx\ln x terms cancel each other out in the expression lnxln3×x2×ln27lnx \frac{\ln x}{\ln 3} \times x^2 \times -\frac{\ln 27}{\ln x}.

Thus, it becomes:

ln27ln3x2+4x+6=0-\frac{\ln 27}{\ln 3} x^2 + 4x + 6 = 0

The value of ln27ln3-\frac{\ln 27}{\ln 3} is actually log327=3-\log_3 27 = -3 because 27=3327 = 3^3.

Therefore, the simplified equation is:

3x2+4x+6=0-3x^2 + 4x + 6 = 0

Step 3: Solve the quadratic equation.

Rearrange it to 3x24x6=03x^2 - 4x - 6 = 0.

Apply the quadratic formula: x=b±b24ac2ax = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}.

Here, a=3a = 3, b=4b = -4, c=6c = -6.

So, the solution becomes:

x=4±(4)24×3×(6)2×3x = \frac{4 \pm \sqrt{(-4)^2 - 4 \times 3 \times (-6)}}{2 \times 3}

This simplifies to:

x=4±16+726x = \frac{4 \pm \sqrt{16 + 72}}{6}

x=4±886x = \frac{4 \pm \sqrt{88}}{6}

Simplify 88=4×22=222\sqrt{88} = \sqrt{4 \times 22} = 2\sqrt{22}.

Thus,

x=4±2226x = \frac{4 \pm 2\sqrt{22}}{6}

Simplifying further gives us:

x=2±223x = \frac{2 \pm \sqrt{22}}{3}

The valid positive solution (since logarithms are not satisfied with negative bases) is:

x=23+223x = \frac{2}{3} + \frac{\sqrt{22}}{3}

Therefore, the correct answer is choice 33: 23+223 \frac{2}{3}+\frac{\sqrt{22}}{3} .

Answer

23+223 \frac{2}{3}+\frac{\sqrt{22}}{3}