Newton Root 75C2A6
1. **State the problem:** We want to find the real root of the equation $x \log_{10} x = 1.2$ using Newton's iterative method, accurate to five decimal places.
2. **Rewrite the equation:** Define the function
$$f(x) = x \log_{10} x - 1.2$$
We want to find $x$ such that $f(x) = 0$.
3. **Newton's method formula:**
$$x_{n+1} = x_n - \frac{f(x_n)}{f'(x_n)}$$
where $f'(x)$ is the derivative of $f(x)$.
4. **Find the derivative:**
Recall that $\frac{d}{dx} \log_{10} x = \frac{1}{x \ln 10}$.
So,
$$f'(x) = \log_{10} x + x \cdot \frac{1}{x \ln 10} = \log_{10} x + \frac{1}{\ln 10}$$
5. **Choose an initial guess:**
Since $x \log_{10} x = 1.2$, try $x=2$:
$2 \times \log_{10} 2 \approx 2 \times 0.3010 = 0.602 < 1.2$, so try $x=5$:
$5 \times \log_{10} 5 \approx 5 \times 0.6990 = 3.495 > 1.2$.
So root lies between 2 and 5. Start with $x_0 = 3$.
6. **Iterate:**
Calculate $x_1$:
$$f(3) = 3 \log_{10} 3 - 1.2 = 3 \times 0.4771 - 1.2 = 1.4313 - 1.2 = 0.2313$$
$$f'(3) = \log_{10} 3 + \frac{1}{\ln 10} = 0.4771 + 0.4343 = 0.9114$$
$$x_1 = 3 - \frac{0.2313}{0.9114} = 3 - 0.2539 = 2.7461$$
Calculate $x_2$:
$$f(2.7461) = 2.7461 \log_{10} 2.7461 - 1.2 = 2.7461 \times 0.4383 - 1.2 = 1.204 - 1.2 = 0.004$$
$$f'(2.7461) = 0.4383 + 0.4343 = 0.8726$$
$$x_2 = 2.7461 - \frac{0.004}{0.8726} = 2.7461 - 0.00458 = 2.7415$$
Calculate $x_3$:
$$f(2.7415) = 2.7415 \log_{10} 2.7415 - 1.2 = 2.7415 \times 0.4375 - 1.2 = 1.1999 - 1.2 = -0.0001$$
$$f'(2.7415) = 0.4375 + 0.4343 = 0.8718$$
$$x_3 = 2.7415 - \frac{-0.0001}{0.8718} = 2.7415 + 0.00011 = 2.7416$$
Calculate $x_4$:
$$f(2.7416) = 2.7416 \log_{10} 2.7416 - 1.2 \approx 0$$
The value has converged to five decimal places.
7. **Final answer:**
$$\boxed{2.74160}$$
This is the root of $x \log_{10} x = 1.2$ correct to five decimal places.