Solve the equation $3^{2x} - 30 = 3^x$.

AlgebraExponential EquationsQuadratic EquationsLogarithmsChange of Base
2025/4/18

1. Problem Description

Solve the equation 32x30=3x3^{2x} - 30 = 3^x.

2. Solution Steps

Let y=3xy = 3^x. Then 32x=(3x)2=y23^{2x} = (3^x)^2 = y^2.
The given equation 32x30=3x3^{2x} - 30 = 3^x can be rewritten as y230=yy^2 - 30 = y.
Rearranging the terms, we have a quadratic equation: y2y30=0y^2 - y - 30 = 0.
We can factor this equation as (y6)(y+5)=0(y - 6)(y + 5) = 0.
So, y=6y = 6 or y=5y = -5.
Since y=3xy = 3^x, we have 3x=63^x = 6 or 3x=53^x = -5.
However, 3x3^x is always positive, so 3x=53^x = -5 has no real solution.
For 3x=63^x = 6, we can take the logarithm base 3 of both sides: x=log36x = \log_3 6.
Using the change of base formula, we can write x=ln6ln3x = \frac{\ln 6}{\ln 3}.
We can also express the solution as x=log36=log3(23)=log32+log33=log32+1x = \log_3 6 = \log_3 (2 \cdot 3) = \log_3 2 + \log_3 3 = \log_3 2 + 1.

3. Final Answer

x=log36x = \log_3 6

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