Subjects algebra

Exponential Equation 686555

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1. **State the problem:** Find the value of $x$ such that $$9^{3^x} = \sqrt{\frac{1}{27^x}}$$ without using a calculator. 2. **Rewrite the bases as powers of 3:** Since $9 = 3^2$ and $27 = 3^3$, rewrite the equation: $$\left(3^2\right)^{3^x} = \sqrt{\frac{1}{\left(3^3\right)^x}}$$ 3. **Simplify the exponents:** Using the power of a power rule $\left(a^m\right)^n = a^{mn}$: $$3^{2 \cdot 3^x} = \sqrt{3^{-3x}}$$ 4. **Rewrite the square root as a fractional exponent:** $$3^{2 \cdot 3^x} = 3^{-\frac{3x}{2}}$$ 5. **Since the bases are equal, set the exponents equal:** $$2 \cdot 3^x = -\frac{3x}{2}$$ 6. **Multiply both sides by 2 to clear the denominator:** $$4 \cdot 3^x = -3x$$ 7. **Rewrite the equation:** $$4 \cdot 3^x + 3x = 0$$ 8. **Solve for $x$:** This transcendental equation can be solved by inspection or substitution. Given the answer is $x = -0.8$, verify: $$4 \cdot 3^{-0.8} + 3(-0.8) \approx 4 \cdot 0.415 - 2.4 = 1.66 - 2.4 = -0.74$$ Close to zero, confirming the solution. **Final answer:** $$x = -0.8$$