Problem: Use Newton-Raphson method to evaluate $\sqrt{13}$ correct up to $4$ decimal places.
Solution: e want to find the value of $\sqrt{13}$ by Newton-Raphson's method. For that, take the function $f(x) = x^2 - 13$. Clearly, one of the roots of the equation $f(x) = 0$ is $\sqrt{13}$. We will approximate this using the Newton-Raphson method. We have
\[
f(x) = x^2 - 13 \quad \text{and} \quad f'(x) = 2x.
\]
Thus, the Newton-Raphson iteration scheme will be
\begin{align*}
x_{n+1} & = x_n - \frac{f(x_n)}{f'(x_n)} \\
& = x_n - \frac{x_n^2 - 13}{2 x_n}, \quad n \geq 0.
\end{align*}
We will start with an initial guess of $x_0 = 1$. Since $f'(1) = 2 \neq 0$, this guess is a valid guess.
-
First iteration: $x_0 = 1$.
\[
x_1 = x_0 - \frac{x_0^2 - 13}{2 x_0} = 7.
\]
-
Second iteration: $x_1 = 7$.
\[
x_2 = x_1 - \frac{x_1^2 - 13}{2 x_1} = 4.4285714.
\]
-
Third iteration: $x_2 = 4.4285714$.
\[
x_3 = x_2 - \frac{x_2^2 - 13}{2 x_2} = 3.6820276.
\]
-
Fourth iteration: $x_3 = 3.6820276$.
\[
x_4 = x_3 - \frac{x_3^2 - 13}{2 x_3} = 3.606345.
\]
-
Fifth iteration: $x_4 = 3.606345$.
\[
x_5 = x_4 - \frac{x_4^2 - 13}{2 x_4} = 3.605551.
\]
-
Sixth iteration: $x_5 = 3.605551$.
\[
x_6 = x_5 - \frac{x_5^2 - 13}{2 x_5} = 3.605551.
\]
Thus, the value $\sqrt{13}$ correct to 4 decimal places is $3.6055$.