Solve the Logarithmic Equation: log₄(x²+8x+1)/log₄8 = 2

Question

log4(x2+8x+1)log48=2 \frac{\log_4(x^2+8x+1)}{\log_48}=2

x=? x=\text{?}

Video Solution

Solution Steps

00:00 Find X
00:04 Use the formula for dividing logarithms
00:11 Get the logarithm of the numerator with base of denominator
00:15 Use this formula in our exercise
00:25 Solve the logarithm to find X
00:30 Arrange the equation
00:45 Use the root formula to find possible solutions
00:55 Calculate and solve
01:20 There will always be 2 solutions, addition and subtraction
01:26 And this is the solution to the question

Step-by-Step Solution

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

  • Step 1: Simplify the given expression using logarithmic identities.
  • Step 2: Solve the resulting quadratic equation for x x .

Now, let's work through each step:

Step 1: We start with the equation:

log4(x2+8x+1)log48=2 \frac{\log_4(x^2+8x+1)}{\log_4 8} = 2

We know that log48=32 \log_4 8 = \frac{3}{2} , since 8=43/2 8 = 4^{3/2} . Thus, we can rewrite the equation as:

log4(x2+8x+1)=2×32=3 \log_4(x^2+8x+1) = 2 \times \frac{3}{2} = 3

Applying the property of logarithms that states logba=ca=bc \log_b a = c \Rightarrow a = b^c , we have:

x2+8x+1=43=64 x^2 + 8x + 1 = 4^3 = 64

Step 2: Solve the resulting quadratic equation:

x2+8x+1=64 x^2 + 8x + 1 = 64

Subtract 64 from both sides to bring the equation to standard form:

x2+8x+164=0 x^2 + 8x + 1 - 64 = 0

x2+8x63=0 x^2 + 8x - 63 = 0

Now, apply the quadratic formula, x=b±b24ac2a x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a} , where a=1 a = 1 , b=8 b = 8 , and c=63 c = -63 :

x=8±8241(63)21 x = \frac{-8 \pm \sqrt{8^2 - 4 \cdot 1 \cdot (-63)}}{2 \cdot 1}

x=8±64+2522 x = \frac{-8 \pm \sqrt{64 + 252}}{2}

x=8±3162 x = \frac{-8 \pm \sqrt{316}}{2}

Simplify 316 \sqrt{316} as 794=279 \sqrt{79 \cdot 4} = 2\sqrt{79} :

x=8±2792 x = \frac{-8 \pm 2\sqrt{79}}{2}

Thus, x=4±79 x = -4 \pm \sqrt{79} .

Therefore, the solution to the equation is x=4±79 x = -4 \pm \sqrt{79} .

Answer

4±79 -4\pm\sqrt{79}