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solve for xx if log10(3x+1)+log10(2x5)=0\log_{10}(3x+1) + \log_{10}(2x-5)=0

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Q. solve for xx if log10(3x+1)+log10(2x5)=0\log_{10}(3x+1) + \log_{10}(2x-5)=0
  1. Combine Logarithmic Expressions: Combine the logarithmic expressions using the product rule for logarithms, which states that log(a)+log(b)=log(ab)\log(a) + \log(b) = \log(ab).log10(3x+1)+log10(2x5)=0\log_{10}(3x+1) + \log_{10}(2x-5) = 0log10((3x+1)(2x5))=0\log_{10}((3x+1)(2x-5)) = 0
  2. Convert to Exponential Form: Convert the logarithmic equation to its exponential form. Since log10(y)=x\log_{10}(y) = x is equivalent to 10x=y10^x = y, we can write:\newline100=(3x+1)(2x5)10^0 = (3x+1)(2x-5)
  3. Simplify Exponential Expression: Simplify the exponential expression, knowing that 100=110^0 = 1. \newline1=(3x+1)(2x5)1 = (3x+1)(2x-5)
  4. Expand Equation: Expand the right side of the equation.\newline1=6x215x+2x51 = 6x^2 - 15x + 2x - 5\newline1=6x213x51 = 6x^2 - 13x - 5
  5. Set Quadratic Equation to Zero: Move all terms to one side to set the quadratic equation to zero.\newline0=6x213x510 = 6x^2 - 13x - 5 - 1\newline0=6x213x60 = 6x^2 - 13x - 6
  6. Factor or Use Quadratic Formula: Factor the quadratic equation, if possible, or use the quadratic formula to find the values of xx. The quadratic formula is x=b±b24ac2ax = \frac{-b \pm \sqrt{b^2-4ac}}{2a}. In this case, a=6a = 6, b=13b = -13, and c=6c = -6.
    Discriminant: Δ=b24ac=(13)24(6)(6)=169+144=313\Delta = b^2 - 4ac = (-13)^2 - 4(6)(-6) = 169 + 144 = 313
    Since the discriminant is positive, there are two real solutions.
  7. Calculate Solutions: Calculate the solutions using the quadratic formula.\newlinex=(13)±31326x = \frac{-(-13) \pm \sqrt{313}}{2 \cdot 6}\newlinex=13±31312x = \frac{13 \pm \sqrt{313}}{12}
  8. Check Validity of Solutions: Check for extraneous solutions by plugging the values of xx back into the original logarithmic expressions to ensure that the arguments of the logarithms are positive.\newlineFor x=13+31312x = \frac{13 + \sqrt{313}}{12}:\newline3x+1=3(13+31312)+1>03x+1 = 3\left(\frac{13 + \sqrt{313}}{12}\right) + 1 > 0\newline2x5=2(13+31312)5>02x-5 = 2\left(\frac{13 + \sqrt{313}}{12}\right) - 5 > 0\newlineBoth expressions are positive, so this is a valid solution.
  9. Check Second Solution: Check the second solution for x=1331312x = \frac{13 - \sqrt{313}}{12}:3x+1=3(1331312)+13x+1 = 3\left(\frac{13 - \sqrt{313}}{12}\right) + 12x5=2(1331312)52x-5 = 2\left(\frac{13 - \sqrt{313}}{12}\right) - 5We need to check if these expressions are positive.
  10. Check Second Solution: Check the second solution for x=1331312x = \frac{13 - \sqrt{313}}{12}:
    3x+1=3(1331312)+13x+1 = 3\left(\frac{13 - \sqrt{313}}{12}\right) + 1
    2x5=2(1331312)52x-5 = 2\left(\frac{13 - \sqrt{313}}{12}\right) - 5
    We need to check if these expressions are positive.Calculate the expressions to ensure they are positive.
    3x+1=3(1331312)+13x+1 = 3\left(\frac{13 - \sqrt{313}}{12}\right) + 1
    This expression is positive because 313\sqrt{313} is less than 1313, so (13313)(13 - \sqrt{313}) is positive, and multiplying by 33 and adding 11 keeps it positive.
    2x5=2(1331312)52x-5 = 2\left(\frac{13 - \sqrt{313}}{12}\right) - 5
    This expression is negative because 313\sqrt{313} is greater than 3x+1=3(1331312)+13x+1 = 3\left(\frac{13 - \sqrt{313}}{12}\right) + 111, so (13313)(13 - \sqrt{313}) is negative, and multiplying by 3x+1=3(1331312)+13x+1 = 3\left(\frac{13 - \sqrt{313}}{12}\right) + 133 and subtracting 3x+1=3(1331312)+13x+1 = 3\left(\frac{13 - \sqrt{313}}{12}\right) + 144 keeps it negative.
    Since 3x+1=3(1331312)+13x+1 = 3\left(\frac{13 - \sqrt{313}}{12}\right) + 155 is negative, this solution is not valid for the logarithmic equation.

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