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Can the limit be found without using L'hospital rule?

lim x --> 1

[ √(x) - x² ] ÷ [ 1 - √(x) ]

Is it possible to solve this limit without using L'hospital rule, since it hasn't been taught in class yet?

Thank you

4 Answers

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  • 2 years ago
    Favorite Answer

    lim x --> 1, [ √(x) - x² ] ÷ [ 1 - √(x) ] = lim x --> 1, [ √(x) - x² ] [ 1 + √(x) ]÷ [ 1 - √(x) ][ 1 + √(x) ]

    = lim x --> 1,√(x) [ 1 - x√(x)] [ 1 + √(x) ]÷ (1 - x) = lim x --> 1, √(x) [ 1+ √(x) -x√(x) - x²] /(1-x)

    =lim x --> 1,√(x){(1-x)(1+x)+(1-x)√(x)}/(1-x) = lim x --> 1,√(x){(1+x)+√(x)} =√(1){(1+1)+√(1)} = 3

  • Anonymous
    2 years ago

    u = √x

    [ √(x) - x² ] ÷ [ 1 - √(x) ]

    = (u - u⁴)/(1-u)

    =[u(1 –u)(1 + u + u²)]/(1 –u)

    =u(1 + u + u²) (u ≠ 1)

    Lim (u → 1)[ u(1 + u + u²)] =2(1 + 1 + 1) = 3.

    [u → 1 as x → 1].

  • 2 years ago

    .

    [ √(x) - x² ] / [ 1 - √(x) ]

    let t = √x

    ∴ x = t²

    [ √(x) - x² ] / [ 1 - √(x) ]

    = ( t - (t²)² ) / ( 1 - t )

    = ( t - t⁴ ) / ( 1 - t )

    = t ( 1 - t³ ) / ( 1 - t ) but difference of cubes (1 - t³ ) = ( 1 - t )( 1 + t + t² )

    = t ( 1 - t )( 1 + t + t² ) / ( 1 - t ) cancel out the 1 - t

    = t ( 1 + t + t² )

    = √x ( 1 + √x + x )

    lim x➝1 { √x ( 1 + √x + x ) }

    = √1 ( 1 + √1 + 1 )

    = 3

  • Let sqrt(x) = u

    (u - u^4) / (1 - u) =>

    u * (1 - u^3) / (1 - u) =>

    u * (1 - u) * (1 + u + u^2) / (1 - u) =>

    u * (1 + u + u^2) =>

    sqrt(x) * (1 + sqrt(x) + x)

    x goes to 1

    sqrt(1) * (1 + sqrt(1) + 1) =>

    1 * (1 + 1 + 1) =>

    3

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