Use logarithms to solve the equation \(5^{3-2x} = 4(7^x)\), giving your answer correct to 3 decimal places.
Solution
Start by taking the natural logarithm of both sides of the equation:
\(\ln(5^{3-2x}) = \ln(4 \cdot 7^x)\)
Apply the logarithm of a product rule: \(\ln(a \cdot b) = \ln a + \ln b\):
\(\ln(5^{3-2x}) = \ln 4 + \ln(7^x)\)
Apply the power rule: \(\ln(a^b) = b \ln a\):
\((3-2x) \ln 5 = \ln 4 + x \ln 7\)
Expand and rearrange to form a linear equation in \(x\):
\(3 \ln 5 - 2x \ln 5 = \ln 4 + x \ln 7\)
Combine like terms:
\(3 \ln 5 - \ln 4 = x \ln 7 + 2x \ln 5\)
Factor out \(x\):
\(3 \ln 5 - \ln 4 = x(\ln 7 + 2 \ln 5)\)
Solve for \(x\):
\(x = \frac{3 \ln 5 - \ln 4}{\ln 7 + 2 \ln 5}\)
Calculate the value of \(x\) to three decimal places:
\(x \approx 0.666\)
Log in to record attempts.