The problem is to solve the exponential equation $5 \times 2^{x-1} = 2 \times 5^{2x}$ for $x$.

AlgebraExponential EquationsLogarithmsEquation SolvingAlgebraic Manipulation
2025/4/23

1. Problem Description

The problem is to solve the exponential equation 5×2x1=2×52x5 \times 2^{x-1} = 2 \times 5^{2x} for xx.

2. Solution Steps

First, divide both sides of the equation by 10, or equivalently, by 5×25 \times 2:
5×2x15×2=2×52x5×2\frac{5 \times 2^{x-1}}{5 \times 2} = \frac{2 \times 5^{2x}}{5 \times 2}
This simplifies to
2x12=52x5\frac{2^{x-1}}{2} = \frac{5^{2x}}{5}
Then, using the rule aman=amn\frac{a^m}{a^n} = a^{m-n}, we have
2x11=52x12^{x-1-1} = 5^{2x-1}
2x2=52x12^{x-2} = 5^{2x-1}
Now, take the logarithm of both sides (using any base, but the natural logarithm is convenient):
ln(2x2)=ln(52x1)\ln(2^{x-2}) = \ln(5^{2x-1})
Using the logarithm property ln(ab)=bln(a)\ln(a^b) = b \ln(a), we get
(x2)ln(2)=(2x1)ln(5)(x-2)\ln(2) = (2x-1)\ln(5)
xln(2)2ln(2)=2xln(5)ln(5)x \ln(2) - 2 \ln(2) = 2x \ln(5) - \ln(5)
Now, rearrange the terms to isolate xx:
2xln(5)xln(2)=ln(5)2ln(2)2x \ln(5) - x \ln(2) = \ln(5) - 2\ln(2)
x(2ln(5)ln(2))=ln(5)2ln(2)x (2 \ln(5) - \ln(2)) = \ln(5) - 2\ln(2)
So, we have
x=ln(5)2ln(2)2ln(5)ln(2)x = \frac{\ln(5) - 2\ln(2)}{2 \ln(5) - \ln(2)}
Using the property aln(b)=ln(ba)a \ln(b) = \ln(b^a), we can rewrite the equation as
x=ln(5)ln(22)ln(52)ln(2)x = \frac{\ln(5) - \ln(2^2)}{\ln(5^2) - \ln(2)}
x=ln(5)ln(4)ln(25)ln(2)x = \frac{\ln(5) - \ln(4)}{\ln(25) - \ln(2)}
Using the property ln(a)ln(b)=ln(ab)\ln(a) - \ln(b) = \ln(\frac{a}{b}), we get
x=ln(54)ln(252)x = \frac{\ln(\frac{5}{4})}{\ln(\frac{25}{2})}
Therefore,
x=ln(1.25)ln(12.5)x = \frac{\ln(1.25)}{\ln(12.5)}
Using a calculator, we can approximate the values:
ln(1.25)0.22314\ln(1.25) \approx 0.22314
ln(12.5)2.52573\ln(12.5) \approx 2.52573
x0.223142.525730.08835x \approx \frac{0.22314}{2.52573} \approx 0.08835
However, let us stick to the exact form:
x=ln(5)2ln(2)2ln(5)ln(2)x = \frac{\ln(5) - 2\ln(2)}{2\ln(5) - \ln(2)}

3. Final Answer

x=ln(5)2ln(2)2ln(5)ln(2)x = \frac{\ln(5) - 2\ln(2)}{2\ln(5) - \ln(2)}

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