Taylor Series Third Term 397Abd
1. The problem asks for the third term in the Taylor series expansion of a function $f(x)$ around the point $a$.
2. The Taylor series expansion of $f(x)$ about $a$ is given by:
$$f(x) = f(a) + f'(a)(x-a) + \frac{f''(a)}{2!}(x-a)^2 + \cdots$$
3. The first term is $f(a)$, the second term is $f'(a)(x-a)$, and the third term is:
$$\frac{f''(a)}{2}(x-a)^2$$
4. This term comes from the formula for the $n$th term in the Taylor series:
$$\frac{f^{(n)}(a)}{n!}(x-a)^n$$
where $n=2$ for the third term (since the series starts at $n=0$).
5. Among the options given:
- (a) is incorrect because it multiplies by $(x-a)$ instead of $(x-a)^2$ and divides by 2 incorrectly.
- (b) is incorrect because it lacks division by 2 and the square on $(x-a)$.
- (c) is correct: $\frac{f''(a)}{2}(x-a)^2$ matches the third term.
- (d) is incorrect because it lacks division by 2.
Final answer: (c) $\frac{f''(a)}{2}(x-a)^2$