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Math Help - Area under curve question

  1. #1
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    Area under curve question

    Ok, so the equation is y=(x^2-1)e^x, y=0, x=-1, x=1, problem is to find area under the curve. That's fine, but this is actually the first one I'm doing where the area in question is /under/ the X-axis, since I'm in calc 2 now.

    I ended up getting x^2e^x - e^x - 2xe^x + 2e^x which simplified to e^x (x^2 -2x +1) which I evaluated from -1 to 1. The problem is that my answer came out to be -4/e which is a negative value, which obviously can't be for area. In this instance, did I forget a step somewhere or do you just change the sign of the answer? Thanks!
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  2. #2
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    Quote Originally Posted by emttim84 View Post
    Ok, so the equation is y=(x^2-1)e^x, y=0, x=-1, x=1, problem is to find area under the curve. That's fine, but this is actually the first one I'm doing where the area in question is /under/ the X-axis, since I'm in calc 2 now.

    I ended up getting x^2e^x - e^x - 2xe^x + 2e^x which simplified to e^x (x^2 -2x +1) which I evaluated from -1 to 1. The problem is that my answer came out to be -4/e which is a negative value, which obviously can't be for area. In this instance, did I forget a step somewhere or do you just change the sign of the answer? Thanks!
    You did do it right....the negative simply means the area is below the x-axis
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