Math Problem Statement

Write out the first five terms of the Taylor series for √x centered at x = 1.

Solution

To find the Taylor series for f(x)=xf(x) = \sqrt{x} centered at x=1x = 1, we use the formula for a Taylor series expansion:

f(x)=n=0f(n)(1)n!(x1)nf(x) = \sum_{n=0}^{\infty} \frac{f^{(n)}(1)}{n!} (x - 1)^n

We need to calculate the first few derivatives of f(x)=xf(x) = \sqrt{x} at x=1x = 1 and evaluate them at x=1x = 1.

  1. First, the function itself: f(x)=x=x1/2f(x) = \sqrt{x} = x^{1/2} f(1)=1=1f(1) = \sqrt{1} = 1

  2. First derivative: f(x)=12x1/2f'(x) = \frac{1}{2} x^{-1/2} f(1)=1211/2=12f'(1) = \frac{1}{2} \cdot 1^{-1/2} = \frac{1}{2}

  3. Second derivative: f(x)=14x3/2f''(x) = \frac{-1}{4} x^{-3/2} f(1)=1413/2=14f''(1) = \frac{-1}{4} \cdot 1^{-3/2} = \frac{-1}{4}

  4. Third derivative: f(3)(x)=38x5/2f^{(3)}(x) = \frac{3}{8} x^{-5/2} f(3)(1)=3815/2=38f^{(3)}(1) = \frac{3}{8} \cdot 1^{-5/2} = \frac{3}{8}

  5. Fourth derivative: f(4)(x)=1516x7/2f^{(4)}(x) = \frac{-15}{16} x^{-7/2} f(4)(1)=151617/2=1516f^{(4)}(1) = \frac{-15}{16} \cdot 1^{-7/2} = \frac{-15}{16}

Now, we can plug these values into the Taylor series formula:

f(x)=f(1)+f(1)(x1)+f(1)2!(x1)2+f(3)(1)3!(x1)3+f(4)(1)4!(x1)4+f(x) = f(1) + f'(1)(x - 1) + \frac{f''(1)}{2!}(x - 1)^2 + \frac{f^{(3)}(1)}{3!}(x - 1)^3 + \frac{f^{(4)}(1)}{4!}(x - 1)^4 + \cdots

Substituting the calculated values:

x=1+12(x1)+14(x1)22!+38(x1)33!+1516(x1)44!+\sqrt{x} = 1 + \frac{1}{2}(x - 1) + \frac{-1}{4} \frac{(x - 1)^2}{2!} + \frac{3}{8} \frac{(x - 1)^3}{3!} + \frac{-15}{16} \frac{(x - 1)^4}{4!} + \cdots

Simplifying:

x=1+12(x1)18(x1)2+116(x1)35128(x1)4+\sqrt{x} = 1 + \frac{1}{2}(x - 1) - \frac{1}{8}(x - 1)^2 + \frac{1}{16}(x - 1)^3 - \frac{5}{128}(x - 1)^4 + \cdots

Thus, the first five terms of the Taylor series for x\sqrt{x} centered at x=1x = 1 are:

1+12(x1)18(x1)2+116(x1)35128(x1)41 + \frac{1}{2}(x - 1) - \frac{1}{8}(x - 1)^2 + \frac{1}{16}(x - 1)^3 - \frac{5}{128}(x - 1)^4

Do you want more details or have any questions?

Here are some related questions to expand your understanding:

  1. How do you find higher-order terms in a Taylor series?
  2. What conditions ensure that a Taylor series converges to the original function?
  3. How is a Taylor series related to a Maclaurin series?
  4. Can you compute the Taylor series for x\sqrt{x} around a different center, say x=4x = 4?
  5. How can you use the Taylor series to approximate 1.1\sqrt{1.1}?

Tip: A Taylor series approximates a function around a specific point. The more terms you use, the more accurate the approximation near that point.

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Math Problem Analysis

Mathematical Concepts

Taylor Series
Derivatives
Square Root Function

Formulas

f(x) = ∑(f^(n)(a) / n!) * (x - a)^n
f(x) = √x = x^(1/2)
f'(x) = 1/2 * x^(-1/2)
f''(x) = -1/4 * x^(-3/2)

Theorems

Taylor Series Expansion

Suitable Grade Level

Undergraduate Calculus