Solve: $\rm 3^x + \frac{1}{3^x} = 9 \frac{1}{9}$
Solution
Given
\( \rm (3^x + \frac{1}{3^x} = 9 \frac{1}{9})\)
Let \( \rm a = 3^x\). Substituting the value of \(a\) in the equation gives us:
\(\rm a + \frac{1}{a} = 9 \frac{1}{9}\)
\( \rm a + \frac{1}{a} = \frac{9 \cdot 9 + 1}{9}\)
\( \rm a + \frac{1}{a} = \frac{82}{9}\)
Multiplying both sides of the equation by \(a\), we get:
\( \rm a \cdot a + \frac{1}{a} \cdot a = \frac{82}{9} \cdot a\)
\( \rm a^2 + 1 = \frac{82a}{9}\)
Multiplying both sides of the equation by \(9\), we get:
\( \rm 9a^2 + 9 = 82a\)
Subtracting \(82a\) from both sides of the equation, we get:
\( \rm 9a^2 - 82a + 9 = 82a - 82a\)
\( \rm 9a^2 - 82a + 9 = 0\)
The above equation is quadratic in \(a\). We use the factorization method to solve it:
\(\rm 9a^2 - (81 + 1)a + 9 = 0\)
\(\rm 9a^2 - 81a - a + 9 = 0\)
\(\rm 9a (a - 9) - 1 (a - 9) = 0\)
\(\rm (9a - 1)(a - 9) = 0\)
Either:
\(\rm 9a - 1 = 0\)
\(\rm 9a = 1\)
\(\rm a = \frac{1}{9}\)
Substituting the value, \(a = 3^x\), we get:
\(\rm 3^x = \frac{1}{3^2}\)
\(\rm 3^x = 3^{-2}\)
\(\rm \therefore x = -2\)
Or:
\(\rm a - 9 = 0\)
\(\rm a = 9\)
Substituting the value, \(a = 3^x\), we get:
\(\rm 3^x = 3^2\)
\(\rm \therefore x = 2\)
Hence, the required values of \(x\) are {-2, 2}.