Solving Integral of x|x| from -1 to 1

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In summary, the integral of x|x|dx from -1 to 1 is equal to zero. This can be explained by using the definition of absolute value and splitting the integral into positive and negative parts.
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olds442
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Homework Statement


integral of x|x|dx.. [-1,1]


The Attempt at a Solution



when graphing it, it is even (looks like the cubic function) and would be 0... but I am having problems convincing myself of this. i checked it out using my calculator, and it just gives back x|x|.. i know if you do the integral of abs x you would split it up into positive and negative parts and all that.. but this is obviously different since it goes below y=0...
 
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  • #2
You would still split it up and add the integral for x>0 up with the one for x<0.
 
  • #3
olds442 said:

The Attempt at a Solution



when graphing it, it is even (looks like the cubic function) and would be 0...

I think you mean it's an odd function. And the definite integral from -a to a should give you zero.


but I am having problems convincing myself of this. i checked it out using my calculator, and it just gives back x|x|.. i know if you do the integral of abs x you would split it up into positive and negative parts and all that.. but this is obviously different since it goes below y=0...

If you use the definition for absolute value,

|x| = x for x => 0 , -x for x < 0 ,

then your integrand is

x·|x| = x^2 for x => 0 , -(x^2) for x < 0 .

That will explain the graph and the result for your definite integral.
 

1. What is the definition of an integral?

An integral is a mathematical concept that is used to determine the area under a curve in a given interval. It is essentially the inverse operation of differentiation, which is used to find the slope of a curve at a specific point.

2. What is the significance of the absolute value function in this integral?

The absolute value function is used to ensure that the area under the curve is always positive. This is necessary because the integral of a function can be negative if the curve dips below the x-axis. Using the absolute value function eliminates this possibility.

3. Why is the interval from -1 to 1 in this integral?

The interval from -1 to 1 is used because it encompasses the entire domain of the absolute value function. This ensures that the entire curve is taken into account when calculating the area under it.

4. How do you solve this integral?

To solve this integral, you can break it into two separate integrals, one from -1 to 0 and one from 0 to 1. In each integral, you can use the fundamental theorem of calculus and the power rule for integration to find the antiderivative. Then, you can plug in the limits of integration and subtract the results to find the final answer.

5. What is the final result of this integral?

The final result of this integral is 0. This is because the area under the curve from -1 to 0 is equal to the area under the curve from 0 to 1, but with opposite signs due to the absolute value function. Therefore, the two areas cancel each other out and the overall integral equals 0.

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