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Question
Math
Posted 7 months ago
Find the Maclaurin series for the function f(x)=cos(x)sin(x)f(x) = cos(x) sin(x) up to the fourth order term.
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Answer from Sia
Posted 7 months ago
Solution by Steps
step 1
To find the Maclaurin series for f(x)=cos(x)sin(x)f(x) = \cos(x) \sin(x) up to the fourth order term, we start by expanding both cos(x)\cos(x) and sin(x)\sin(x) using their Maclaurin series
step 2
The Maclaurin series for cos(x)\cos(x) is: cos(x)=1x22!+x44!+O(x6) \cos(x) = 1 - \frac{x^2}{2!} + \frac{x^4}{4!} + O(x^6)
step 3
The Maclaurin series for sin(x)\sin(x) is: sin(x)=xx33!+O(x5) \sin(x) = x - \frac{x^3}{3!} + O(x^5)
step 4
Multiply the series for cos(x)\cos(x) and sin(x)\sin(x) and collect terms up to x4x^4: cos(x)sin(x)=(1x22!+x44!)(xx33!) \cos(x) \sin(x) = \left(1 - \frac{x^2}{2!} + \frac{x^4}{4!}\right) \left(x - \frac{x^3}{3!}\right)
step 5
Expanding and simplifying the product: cos(x)sin(x)=xx32x36+x524+O(x5) \cos(x) \sin(x) = x - \frac{x^3}{2} - \frac{x^3}{6} + \frac{x^5}{24} + O(x^5) =x2x33+O(x5) = x - \frac{2x^3}{3} + O(x^5)
Answer
The Maclaurin series for f(x)=cos(x)sin(x)f(x) = \cos(x) \sin(x) up to the fourth order term is: f(x)=x2x33+O(x5) f(x) = x - \frac{2x^3}{3} + O(x^5)
Key Concept
Maclaurin series expansion
Explanation
The Maclaurin series expansion is a way to represent a function as an infinite sum of terms calculated from the values of its derivatives at a single point (usually zero). In this case, we expanded cos(x)\cos(x) and sin(x)\sin(x) and multiplied the series to find the series for cos(x)sin(x)\cos(x) \sin(x).

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