We are given two equations: $\log y = 2 \log x + 1$ and $2y = 9x - 1$. We need to solve for $x$ and $y$. We are assuming base 10 logarithm.

AlgebraLogarithmsQuadratic EquationsSystems of EquationsSubstitutionFactorization
2025/3/17

1. Problem Description

We are given two equations:
logy=2logx+1\log y = 2 \log x + 1 and 2y=9x12y = 9x - 1. We need to solve for xx and yy. We are assuming base 10 logarithm.

2. Solution Steps

First, let's rewrite the first equation using properties of logarithms.
logy=2logx+1\log y = 2 \log x + 1
logy=logx2+log10\log y = \log x^2 + \log 10
logy=log(10x2)\log y = \log (10x^2)
y=10x2y = 10x^2
Now substitute this expression for yy into the second equation:
2y=9x12y = 9x - 1
2(10x2)=9x12(10x^2) = 9x - 1
20x2=9x120x^2 = 9x - 1
20x29x+1=020x^2 - 9x + 1 = 0
Now we have a quadratic equation in xx. We can solve this using the quadratic formula or by factoring. Let's try factoring:
20x29x+1=020x^2 - 9x + 1 = 0
(4x1)(5x1)=0(4x - 1)(5x - 1) = 0
So the possible values for xx are x=14x = \frac{1}{4} or x=15x = \frac{1}{5}.
Now we can find the corresponding values for yy using y=10x2y = 10x^2:
If x=14x = \frac{1}{4}, then y=10(14)2=10(116)=1016=58y = 10(\frac{1}{4})^2 = 10(\frac{1}{16}) = \frac{10}{16} = \frac{5}{8}.
If x=15x = \frac{1}{5}, then y=10(15)2=10(125)=1025=25y = 10(\frac{1}{5})^2 = 10(\frac{1}{25}) = \frac{10}{25} = \frac{2}{5}.
Now we check these solutions in the second original equation, 2y=9x12y = 9x - 1.
If x=14x = \frac{1}{4} and y=58y = \frac{5}{8}, then 2y=2(58)=542y = 2(\frac{5}{8}) = \frac{5}{4} and 9x1=9(14)1=9444=549x - 1 = 9(\frac{1}{4}) - 1 = \frac{9}{4} - \frac{4}{4} = \frac{5}{4}. So this solution works.
If x=15x = \frac{1}{5} and y=25y = \frac{2}{5}, then 2y=2(25)=452y = 2(\frac{2}{5}) = \frac{4}{5} and 9x1=9(15)1=9555=459x - 1 = 9(\frac{1}{5}) - 1 = \frac{9}{5} - \frac{5}{5} = \frac{4}{5}. So this solution also works.

3. Final Answer

The solutions are (x,y)=(14,58)(x, y) = (\frac{1}{4}, \frac{5}{8}) and (x,y)=(15,25)(x, y) = (\frac{1}{5}, \frac{2}{5}).

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