EVALUATING LIMITS BY RATIONALIZING

Evaluating limits can be done in the following ways.

  • Applying the given limit directly. While doing so, sometimes there is a chance to get indeterminant forms.

Some of the indeterminant forms are :

0/0, ∞/∞, ∞∞, 0∞

  • After simplification, we can apply the limit.
  • After performing rationalization. 

Conjugate of √a+b is √a-b

Conjugate of √a+√b is √a-√b

Conjugate of b+√a is b - √a

To perform rationalization, we have to multiply numerator and denominator by the conjugate.

Evaluating the given limits :

Problem 1 :

y05+y-5y

Solution:

=y05+y-5y=y05+y-55+y+5y5+y+5=y05+y-5y5+y+5=y0yy5+y+5=y015+y+5=15+5=125×55=510

Problem 2 :

x0x+3-3x

Solution:

=x0x+3-3x=x0x+3-3x+3+3xx+3+3=x0x+3-3xx+3+3=x01x+3+3=13+3=123×33=36

Problem 3 :

x02x+1-1x

Solution:

=x02x+1-1x=x02x+1-12x+1+1x2x+1+1=x02x+1-1x2x+1+1=x022x+1+1=22(0)+1+1=22=1

Problem 4 :

x-3x+7-2x+3

Solution:

=x-3x+7-2x+3=x-3x+7-2x+7+2x+3x+7+2=x-3x+7-4x+3x+7+2=x-3x+3x+3x+7+2=x-31x+7+2=1-3+7+2=14+2=12+2=14

Problem 5 :

x45-x-12-x

Solution:

=x45-x-12-x=x45-x-12-x×2+x2+x=x45-x-12+x(4-x)×5-x+15-x+1=x4(5-x-1)2+x(4-x)5-x+1=x4(4-x)2+x(4-x)5-x+1=x42+x5-x+1=2+45-4+1=2+21+1=42=2

Problem 6 :

x41x-2-4x-4

Solution:

lim x41x-2-4x-4=lim x41x-2×x+2x+2-4x-4=lim x4x+2x-4-4x-4=lim x4x+2-4x-4=lim x4x-2x-4=lim x4x-2x-4×x+2x+2=lim x4x-4(x-4)x+2=lim x41x+2Applying the limit, we get=14+2=14

Problem 7 :

x02x3-x+9

Solution:

=x02x3-x+9=x02x3+x+93-x+93+x+9=x02x3+x+99-x-9=x02x3+x+9-x=x0-23+x+9=-23+0+9=-2(3+3)=-12

Problem 8 :

x0x2+9-2x2+93x2+4-2x2+4

Solution:

=x0x2+9-2x2+93x2+4-2x2+4=x0x2+9-2x2+93x2+4-2x2+4×x2+9+2x2+93x2+4+2x2+4×3x2+4+2x2+4x2+9+2x2+9=x0x2+9-2x2-93x2+4-2x2-4×3x2+4x2+9×2x2+42x2+9=x0-x23x2+4+2x2+4x2x2+9+2x2+9=-0+4+0+40+9+0+9=-2+23+3=-46=-23

Problem 9 :

x0+1x-1x2+x

Solution:

lim x0+1x lim x0+1x lim x0+1x lim x0+1x lim x0+1x lim x0+1x lim x0+1x lim x0+1x lim x0+

Problem 10 :

x016+x-4x

Solution:

=x016+x-4x=x016+x-416+x+4x16+x+4=x016+x-16x16+x+4=x0xx16+x+4=x0116+x+4=116+4=14+4=18

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