Solve for X: Logarithmic Equation with x^4 Base and Multiple Terms

Question

Find X

1logx42×xlogx16+4x2=7x+2 \frac{1}{\log_{x^4}2}\times x\log_x16+4x^2=7x+2

Video Solution

Solution Steps

00:00 Find X
00:04 Find the domain
00:10 Use the formula of 1 divided by log, we'll get the inverse logarithm
00:22 Use the formula for logarithm multiplication, switch between bases
00:37 Solve each logarithm separately and substitute in the exercise
01:07 Collect terms and arrange the equation
01:27 Use the quadratic formula to find possible solutions
01:37 There are always 2 solutions, addition and subtraction
01:42 Check each solution with the domain
01:47 And that's the solution to the question

Step-by-Step Solution

To solve this problem, we'll follow these steps:

  • Simplify the logarithmic expressions using properties of logarithms.
  • Substitute the simplifications into the original expression and simplify algebraically.
  • Solve the resulting equation for the variable x x .

Let's work through these steps in detail:

Step 1: Simplify the logarithmic expressions.
- The expression 1logx42\frac{1}{\log_{x^4}2} can be rewritten using the change of base formula: 1logx42=log244\frac{1}{\log_{x^4}2} = \frac{\log_24}{4}. This comes from recognizing that logx42=14logx2\log_{x^4}2 = \frac{1}{4}\log_x2, hence 1logx42=4log24\frac{1}{\log_{x^4}2} = 4\log_24.

Step 2: Simplify xlogx16x\log_x16.
- Using the property that logx16=4logxx=4\log_x16 = 4\log_xx = 4, we get xlogx16=x×4=4x x\log_x16 = x \times 4 = 4x .

Step 3: Substitute into the original equation.
Substituting these into the original equation 1logx42×xlogx16+4x2=7x+2 \frac{1}{\log_{x^4}2}\times x\log_x16+4x^2=7x+2 , we get:

log24×4x+4x2=7x+2 \log_24 \times 4x + 4x^2 = 7x + 2 .

Step 4: Simplify and solve the equation.
- Knowing that log24×4x=2x\log_24 \times 4x = 2x (since log24=2 \log_24 = 2 ), replace and simplify the equation:

2x+4x2=7x+2 2x + 4x^2 = 7x + 2 .

Rearrange this to:
4x25x2=0 4x^2 - 5x - 2 = 0 .

Step 5: Solve the quadratic equation using the quadratic formula:
The quadratic formula is given by: x=b±b24ac2a x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a} , where a=4 a = 4 , b=5 b = -5 , c=2 c = -2 .

Substitute these values into the formula:

x=(5)±(5)244(2)24 x = \frac{-(-5) \pm \sqrt{(-5)^2 - 4 \cdot 4 \cdot (-2)}}{2 \cdot 4}
x=5±25+328 x = \frac{5 \pm \sqrt{25 + 32}}{8}
x=5±578 x = \frac{5 \pm \sqrt{57}}{8} .

Step 6: Check solution viability.
Since x x needs to be greater than 1 to make all log values valid, choose x=9+1138 x = \frac{-9+\sqrt{113}}{8} (the positive square root).

Therefore, the solution to the problem is x=9+1138 x = \frac{-9+\sqrt{113}}{8} , which matches choice 1 in the provided options.

Answer

9+1138 \frac{-9+\sqrt{113}}{8}


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