Solve Logarithmic Equation: 1/2 log₃(x⁴) = log₃(3x² + 5x + 1)

Question

12log3(x4)=log3(3x2+5x+1) \frac{1}{2}\log_3(x^4)=\log_3(3x^2+5x+1)

x=? x=\text{?}

Video Solution

Solution Steps

00:00 Find X
00:05 Use the logarithm formula for exponents, and move the 0.5 into the logarithm
00:17 Raising to the power of one-half is like taking the square root
00:27 Break down X⁴ into X squared squared
00:32 Square root cancels square
00:34 Substitute in our exercise
00:42 Compare the numbers
00:52 Group terms and arrange the equation
00:57 Use the root formula to find possible solutions
01:12 There are always 2 possible solutions, addition and subtraction
01:27 Find the domain
01:37 And this is the solution to the question

Step-by-Step Solution

To solve the equation 12log3(x4)=log3(3x2+5x+1) \frac{1}{2}\log_3(x^4) = \log_3(3x^2 + 5x + 1) , we will first use the power property of logarithms.

  • Step 1: Apply the power property to the left side: 12log3(x4)=log3(x4)12=log3(x2) \frac{1}{2}\log_3(x^4) = \log_3(x^4)^{\frac{1}{2}} = \log_3(x^2) .

  • Step 2: Now, equating the arguments on both sides, we have: x2=3x2+5x+1 x^2 = 3x^2 + 5x + 1 .

  • Step 3: Rearrange the equation to form a standard quadratic: 0=2x2+5x+1 0 = 2x^2 + 5x + 1 or 2x2+5x+1=0 2x^2 + 5x + 1 = 0 .

  • Step 4: Solve the quadratic using the quadratic formula: x=b±b24ac2a x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a} , where a=2 a = 2 , b=5 b = 5 , and c=1 c = 1 .

  • Step 5: Substitute the coefficients into the quadratic formula:

  • xamp;=5±5242122amp;=5±2584amp;=5±174 \begin{aligned} x &= \frac{-5 \pm \sqrt{5^2 - 4 \cdot 2 \cdot 1}}{2 \cdot 2} \\ &= \frac{-5 \pm \sqrt{25 - 8}}{4} \\ &= \frac{-5 \pm \sqrt{17}}{4} \end{aligned}

Since we need the solutions to keep the arguments of the logarithms positive, we ensure that 3x^2 + 5x + 1 > 0 for values of x x from our solution set.

Thus, the solutions satisfying these conditions are given by x=54±174 x = -\frac{5}{4} \pm \frac{\sqrt{17}}{4} . Therefore, the correct answer is choice 1: 54±174 -\frac{5}{4} \pm \frac{\sqrt{17}}{4} .

Answer

54±174 -\frac{5}{4}\pm\frac{\sqrt{17}}{4}