Subjects calculus

Exponential Limit Fb1438

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Question: top-left: none top-right: none center: $\lim_{x\to\infty}\left(\frac{4^x+9^x}{x}\right)^{1/x}$ bottom-left: $x\to\infty$ bottom-right: none
**Problem:** Evaluate $\lim_{x\to\infty}\left(\frac{4^x+9^x}{x}\right)^{1/x}$. 1. Use the dominant-term rule: when $x\to\infty$, the larger exponential base dominates, so factor out $9^x$. $$\left(\frac{4^x+9^x}{x}\right)^{1/x}=\left(\frac{9^x\left[\left(\frac{4}{9}\right)^x+1\right]}{x}\right)^{1/x}$$ 2. Separate the factors using exponent rules. $$=9\left(\left(\frac{4}{9}\right)^x+1\right)^{1/x}\left(\frac{1}{x}\right)^{1/x}$$ 3. Since $0<\frac{4}{9}<1$, we have $\left(\frac{4}{9}\right)^x\to0$, so the middle factor approaches $1$. $$\left(\left(\frac{4}{9}\right)^x+1\right)^{1/x}\to1$$ 4. Also, $x^{1/x}\to1$, so its reciprocal approaches $1$. $$\left(\frac{1}{x}\right)^{1/x}=\frac{1}{x^{1/x}}\to1$$ 5. Multiply the limiting factors. $$9\cdot1\cdot1=9$$ **Final answer:** $9$.