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Anonymous
Anonymous asked in Science & MathematicsMathematics · 9 years ago

Calc. 2 question! help me please!?

i have no clue to how to start with this integration:

Integration of SquareRoot(2x-x^2) dx

2 Answers

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  • 9 years ago
    Favorite Answer

    I would rewrite by completing the square:

    INT[ sqr(2x-x^2)] dx= INT { sqr[1-(x-1)^2] } dx

    Now use trig substitution,

    Sin(u)= (x-1)/1= x-1

    Sqr[1-(x-1)^2] = cos(u)

    X= sinu + 1

    Dx = cosu du

    INT [ cosu * cosu du]....remember that cos^2(u)= (1/2)(1+ cos(2u))

    = INT [(1/2)* (1+ cos2u) ] du

    = (1/2) [ u + (1/2)sin2u] + C.....remember that sin2u= 2sinucosu

    = (1/2)[ u + sinucosu ] + C

    = (1/2) {sin^-1(x-1) + (x-1)* sqr[1-(x-1)^2]} + C

    Hoping this helps!

  • 9 years ago

    factor out a x.

    sqrt(x(2-x)).

    INT[sqrtx*sqrt(2-x)]

    u^2=x

    2udu=dx

    INT[u*sqrt(2-u^2)du]

    trig sub.

    u=sqrt(2)sinv

    v=theta

    du=sqrt(2)cosv

    INT[sqrt(2)sinv*sqrt(2-2sin^2v) *sqrt(2)cosv dv]

    INT[2sinvcosv*sqrt(2cos^2v) dv]

    INT[2sinvcosv*sqrt(2)*cosv]

    2sqrt(2)*INT[2sinvcos^2v dv]

    u-sub. I am going to use t.

    t=cosv

    dt=-sinvdv

    -2dt=2sindv

    -4sqrt(2)*INT[t^2dt]

    -4sqrt(2)*[1/3*t^3]

    (-4/3)sqrt(2)*cos^3v.

    hower remember

    u=sqrt(2)sinv

    u/sqrt(2)=sinv

    draw a triangle.

    cosv=sqrt[(2-u^2)/2)]

    however remember

    u=sqrtx

    so plug that in and you will have your answer.

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