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Solve the equation log_(2)(4x-3)+log_(2)(3x+5)=3

Solve the equation log2(4x3)+log2(3x+5)=3 \log_{2}(4x-3)+\log_{2}(3x+5)=3

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Q. Solve the equation log2(4x3)+log2(3x+5)=3 \log_{2}(4x-3)+\log_{2}(3x+5)=3
  1. Combine Logs: We can use the property of logarithms that allows us to combine the sum of two logs with the same base into a single log by multiplying the arguments. So, we combine log2(4x3)\log_2(4x-3) and log2(3x+5)\log_2(3x+5) into a single logarithm.\newlinelog2((4x3)(3x+5))=3\log_2((4x-3)(3x+5)) = 3
  2. Exponential Form: Next, we can rewrite the equation in exponential form to eliminate the logarithm. The equation log2(y)=3\log_2(y) = 3 is equivalent to 23=y2^3 = y. \newline(4x3)(3x+5)=23(4x-3)(3x+5) = 2^3
  3. Calculate Right Side: Now we calculate 232^3 to simplify the right side of the equation.\newline(4x3)(3x+5)=8(4x-3)(3x+5) = 8
  4. Expand Left Side: We expand the left side of the equation by multiplying the binomials.\newline4x×3x+4x×53×3x3×5=84x \times 3x + 4x \times 5 - 3 \times 3x - 3 \times 5 = 8\newline12x2+20x9x15=812x^2 + 20x - 9x - 15 = 8
  5. Combine Like Terms: Combine like terms on the left side of the equation. 12x2+11x15=812x^2 + 11x - 15 = 8
  6. Set Equation to Zero: Subtract 88 from both sides to set the equation to zero, which is necessary for solving a quadratic equation.\newline12x2+11x158=012x^2 + 11x - 15 - 8 = 0\newline12x2+11x23=012x^2 + 11x - 23 = 0
  7. Solve Quadratic Equation: Now we need to solve the quadratic equation. This can be done by factoring, completing the square, or using the quadratic formula. The quadratic formula is x=b±b24ac2ax = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}. In this case, a=12a = 12, b=11b = 11, and c=23c = -23.
  8. Calculate Discriminant: We calculate the discriminant b24acb^2 - 4ac to determine if there are real solutions.\newlineDiscriminant = 1124(12)(23)11^2 - 4(12)(-23)\newlineDiscriminant = 121+1104121 + 1104\newlineDiscriminant = 12251225
  9. Apply Quadratic Formula: Since the discriminant is positive, there are two real solutions. We proceed with the quadratic formula.\newlinex=11±122524x = \frac{{-11 \pm \sqrt{1225}}}{{24}}
  10. Calculate Square Root: Calculate the square root of the discriminant. 1225=35\sqrt{1225} = 35
  11. Substitute Square Root: Substitute the square root back into the quadratic formula.\newlinex=11±3524x = \frac{{-11 \pm 35}}{{24}}
  12. Solve for x: Solve for the two possible values of x.\newlinex1=11+3524x_1 = \frac{-11 + 35}{24}\newlinex1=2424x_1 = \frac{24}{24}\newlinex1=1x_1 = 1\newlinex2=113524x_2 = \frac{-11 - 35}{24}\newlinex2=4624x_2 = \frac{-46}{24}\newlinex2=2312x_2 = \frac{-23}{12}
  13. Check Valid Solutions: We must check these solutions to ensure they do not make the argument of the original logarithms negative, as the logarithm of a negative number is undefined.\newlineFor x1=1x_1 = 1:\newline4(1)3=43=14(1) - 3 = 4 - 3 = 1 (positive)\newline3(1)+5=3+5=83(1) + 5 = 3 + 5 = 8 (positive)\newlineFor x2=2312x_2 = -\frac{23}{12}:\newline4\left(-\frac{23}{12}\right) - 3 = -\frac{23}{3} - 3 < 0 (negative)\newline3\left(-\frac{23}{12}\right) + 5 = -\frac{23}{4} + 5 < 0 (negative)\newlinex2=2312x_2 = -\frac{23}{12} is not a valid solution because it makes the arguments of the logarithms negative.
  14. Final Valid Solution: Therefore, the only valid solution is x1=1x_1 = 1.

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