Derivative of x sin x: Why Isn't the Answer x cos x?

In summary, the derivative of f(x) = x sin x is given by the product rule and can be simplified to f'(x) = x cos x + sin x. It represents the instantaneous rate of change and can be used in real-world applications in physics and engineering.
  • #1
bobsmith76
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Homework Statement



differentiate f(x)= x sin x

Homework Equations





The Attempt at a Solution



The answer is x cos x + (sin x) * 1

I thought the derivative of sine was cosine. So why isn't the answer x cos x?
 
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  • #2
Don't forget about the [strike]chain[/strike] product rule:

d/dx f(x)*g(x) = f'(x)g(x) + f(x)g'(x)

In this case: f(x) = sin x & g(x) = x


@vela - thanks for the correction
 
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  • #3
You mean the product rule, not the chain rule.
 
  • #4
good, i got it now, thanks
 

Related to Derivative of x sin x: Why Isn't the Answer x cos x?

1. What is the derivative of f(x) = x sin x?

The derivative of f(x) = x sin x is given by the product rule: f'(x) = x cos x + sin x.

2. How do you find the derivative of a product of two functions?

To find the derivative of a product of two functions, you can use the product rule: (f(x)g(x))' = f'(x)g(x) + f(x)g'(x).

3. Can the derivative of f(x) = x sin x be simplified?

Yes, the derivative of f(x) = x sin x can be simplified to f'(x) = x cos x + sin x.

4. What is the significance of the derivative of f(x) = x sin x?

The derivative of f(x) = x sin x represents the instantaneous rate of change or slope of the function at a specific point. It is also useful in finding critical points, which are important in graphing and optimization problems.

5. How can I use the derivative of f(x) = x sin x in real-world applications?

The derivative of f(x) = x sin x can be used in physics to calculate the velocity of an object that is moving with simple harmonic motion, such as a pendulum. It can also be used in engineering to model and analyze systems with periodic motion, such as springs and circuits.

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