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F
Lv 6
F asked in Science & MathematicsMathematics · 1 decade ago

Problem with an integral?

Hi.

How do I integrate the following function:

∫ (x+1)*sqrt(5-x) dx.

I want to know how to do it using substitution, not integration by parts. Please show how you do it and explain the steps.

Thank you!

2 Answers

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  • ?
    Lv 6
    1 decade ago
    Favorite Answer

    Let u = 5-x ; x = 5-u

    du = -dx

    ∫ (x+1)*√(5-x) dx = ∫ (6-u)*√u *(-du)

    = ∫ (u-6)√u du.

    = ∫ u√u du - ∫ 6√u du

    = ∫ u^(3/2) du - 6∫ u^(1/2) du

    = u^(5/2) /(5/2) - 6u^(3/2) /(3/2) + c

    = (2/5)u^(5/2) - 4u^(3/2) + c

    = (2/5)(5-x)^(5/2) - 4(5-x)^(3/2) + c

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