Math Problem Statement

((2 * log_3(x)) - 4)/(log_3(x/9)) = log_3(x ^ 7) - (1/(log_x(3))) ^ 2 - 8 Find lowest value of X

Solution

We are given the following equation:

2log3(x)4log3(x/9)=log3(x7)(1logx(3))28\frac{2 \log_3(x) - 4}{\log_3(x/9)} = \log_3(x^7) - \left(\frac{1}{\log_x(3)}\right)^2 - 8

Step 1: Simplify the logarithmic expressions

Left side:

2log3(x)4log3(x/9)\frac{2 \log_3(x) - 4}{\log_3(x/9)}

Using the logarithmic property logb(ac)=logb(a)logb(c)\log_b \left(\frac{a}{c}\right) = \log_b(a) - \log_b(c), we can simplify log3(x/9)\log_3(x/9): log3(x9)=log3(x)log3(9)\log_3\left(\frac{x}{9}\right) = \log_3(x) - \log_3(9) Since log3(9)=2\log_3(9) = 2, this becomes: log3(x/9)=log3(x)2\log_3(x/9) = \log_3(x) - 2 Thus, the left-hand side becomes: 2log3(x)4log3(x)2\frac{2 \log_3(x) - 4}{\log_3(x) - 2}

Right side:

log3(x7)(1logx(3))28\log_3(x^7) - \left(\frac{1}{\log_x(3)}\right)^2 - 8 Using the logarithmic power rule logb(an)=nlogb(a)\log_b(a^n) = n \log_b(a), we get: log3(x7)=7log3(x)\log_3(x^7) = 7 \log_3(x)

Next, simplify 1logx(3)\frac{1}{\log_x(3)}. By the change of base formula: logx(3)=1log3(x)\log_x(3) = \frac{1}{\log_3(x)} Thus, 1logx(3)=log3(x)\frac{1}{\log_x(3)} = \log_3(x) and (1logx(3))2=log3(x)2\left(\frac{1}{\log_x(3)}\right)^2 = \log_3(x)^2

Therefore, the right-hand side becomes: 7log3(x)log3(x)287 \log_3(x) - \log_3(x)^2 - 8

Step 2: Set up the equation

The equation is now: 2log3(x)4log3(x)2=7log3(x)log3(x)28\frac{2 \log_3(x) - 4}{\log_3(x) - 2} = 7 \log_3(x) - \log_3(x)^2 - 8

Let y=log3(x)y = \log_3(x), so the equation becomes: 2y4y2=7yy28\frac{2y - 4}{y - 2} = 7y - y^2 - 8

Step 3: Solve for yy

Multiply both sides by y2y - 2 to eliminate the denominator: 2y4=(7yy28)(y2)2y - 4 = (7y - y^2 - 8)(y - 2) Expand the right-hand side: 2y4=(7yy28)(y2)2y - 4 = (7y - y^2 - 8)(y - 2) 2y4=7y214yy3+2y28y+162y - 4 = 7y^2 - 14y - y^3 + 2y^2 - 8y + 16 2y4=y3+9y222y+162y - 4 = -y^3 + 9y^2 - 22y + 16 Move everything to one side: 0=y3+9y224y+200 = -y^3 + 9y^2 - 24y + 20 y39y2+24y20=0y^3 - 9y^2 + 24y - 20 = 0

Step 4: Solve the cubic equation

We now solve y39y2+24y20=0y^3 - 9y^2 + 24y - 20 = 0. Testing small integer values, we find:

For y=2y = 2: 23922+24220=836+4820=02^3 - 9 \cdot 2^2 + 24 \cdot 2 - 20 = 8 - 36 + 48 - 20 = 0 So, y=2y = 2 is a solution.

Step 5: Factor and solve the quadratic

Now factor (y2)(y - 2) out of the cubic equation. Using synthetic division, we factor y39y2+24y20y^3 - 9y^2 + 24y - 20 as: (y2)(y27y+10)=0(y - 2)(y^2 - 7y + 10) = 0 Solving y27y+10=0y^2 - 7y + 10 = 0 using the quadratic formula: y=7±(7)24(1)(10)2(1)=7±49402=7±92y = \frac{7 \pm \sqrt{(-7)^2 - 4(1)(10)}}{2(1)} = \frac{7 \pm \sqrt{49 - 40}}{2} = \frac{7 \pm \sqrt{9}}{2} y=7±32y = \frac{7 \pm 3}{2} So, y=7+32=5ory=732=2y = \frac{7 + 3}{2} = 5 \quad \text{or} \quad y = \frac{7 - 3}{2} = 2

Thus, y=5y = 5 or y=2y = 2.

Step 6: Find xx

Since y=log3(x)y = \log_3(x), we have: log3(x)=5x=35=243\log_3(x) = 5 \quad \Rightarrow \quad x = 3^5 = 243 log3(x)=2x=32=9\log_3(x) = 2 \quad \Rightarrow \quad x = 3^2 = 9

Step 7: Conclusion

The possible values of xx are 9 and 243. Since we are asked for the lowest value, the lowest value of xx is:

9\boxed{9}

Would you like any further details on the solution?

Related Questions:

  1. What is the change of base formula for logarithms?
  2. How do you solve cubic equations by synthetic division?
  3. How do logarithmic properties simplify equations?
  4. What is the significance of the quadratic formula?
  5. How can you verify solutions for logarithmic equations?

Tip:

Always verify each solution to ensure it does not lead to a mathematical inconsistency, especially when dealing with logarithms!

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Math Problem Analysis

Mathematical Concepts

Logarithmic Equations
Cubic Equations
Quadratic Formula
Synthetic Division

Formulas

log_b(a^n) = n * log_b(a)
log_b(a/c) = log_b(a) - log_b(c)
Quadratic formula: (-b ± √(b² - 4ac)) / 2a
Change of base formula: log_b(a) = log_c(a) / log_c(b)

Theorems

Logarithmic Properties
Change of Base Formula
Quadratic Formula

Suitable Grade Level

Grades 10-12