folve the equation \( 1+\log (2 x-9)=\log (3 x+5)-\log 2 \). 27. COMMERCIAI ARITHMETIC (II)
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To solve the equation \( 1+\log (2 x-9)=\log (3 x+5)-\log 2 \), we first use the properties of logarithms to combine the terms on the right side: \[ \log (3 x + 5) - \log 2 = \log \left( \frac{3x + 5}{2} \right). \] Now, rewrite the equation: \[ 1 + \log(2x - 9) = \log\left( \frac{3x + 5}{2} \right). \] We can convert the \(1\) to a logarithmic form: \[ 1 = \log(10), \] which allows us to rewrite the left side as: \[ \log(10) + \log(2x - 9) = \log(10(2x - 9)). \] So the equation becomes: \[ \log(10(2x - 9)) = \log\left( \frac{3x + 5}{2} \right). \] Since the logarithms are equal, we can set their arguments equal to each other: \[ 10(2x - 9) = \frac{3x + 5}{2}. \] Cross-multiply to eliminate the fraction: \[ 20(2x - 9) = 3x + 5. \] Distributing the left side gives: \[ 40x - 180 = 3x + 5. \] Now, isolate \(x\): \[ 40x - 3x = 180 + 5, \] which simplifies to: \[ 37x = 185, \] and dividing through by 37 gives: \[ x = 5. \] Finally, we should verify that our solution is valid by checking the conditions inside the logarithms: - \(2x - 9 = 2(5) - 9 = 10 - 9 = 1 > 0\), - \(3x + 5 = 3(5) + 5 = 15 + 5 = 20 > 0\). Both conditions hold true, confirming that our solution \(x = 5\) is indeed valid.