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i want to fint the lim of this Lim-->4 (x*sqrt(x)-8)/(x-4)    i know its 3 https://graphsketch.com/ but how can prove it? 

 Jan 24, 2016

Best Answer 

 #1
avatar
+15

Find the following limit:
lim_(x->4) (x sqrt(x)-8)/(x-4)

(x sqrt(x)-8)/(x-4) = (x^(3/2)-8)/(x-4):
lim_(x->4) (x^(3/2)-8)/(x-4)

Factor the numerator and denominator:
lim_(x->4) ((sqrt(x)-2) (4+2 sqrt(x)+x))/((sqrt(x)-2) (2+sqrt(x)))

Cancel terms, assuming sqrt(x)-2!=0:
lim_(x->4) (4+2 sqrt(x)+x)/(2+sqrt(x))

lim_(x->4) (4+2 sqrt(x)+x)/(2+sqrt(x))  =  (4+2 sqrt(4)+4)/(2+sqrt(4))  =  3:
Answer: | =3
 

 Jan 24, 2016
 #1
avatar
+15
Best Answer

Find the following limit:
lim_(x->4) (x sqrt(x)-8)/(x-4)

(x sqrt(x)-8)/(x-4) = (x^(3/2)-8)/(x-4):
lim_(x->4) (x^(3/2)-8)/(x-4)

Factor the numerator and denominator:
lim_(x->4) ((sqrt(x)-2) (4+2 sqrt(x)+x))/((sqrt(x)-2) (2+sqrt(x)))

Cancel terms, assuming sqrt(x)-2!=0:
lim_(x->4) (4+2 sqrt(x)+x)/(2+sqrt(x))

lim_(x->4) (4+2 sqrt(x)+x)/(2+sqrt(x))  =  (4+2 sqrt(4)+4)/(2+sqrt(4))  =  3:
Answer: | =3
 

Guest Jan 24, 2016
 #2
avatar+118696 
+10

 Lim-->4 (x*sqrt(x)-8)/(x-4)  

 

limx4(xx8)(x4)=limx4(xx8)(x4)

 

At this point I have learned from our guest.  Thankyou :)  

 

 

=limx4(xx8)(x2)(x+2)  I need to get rid of the x2in the denominatorNow I used algebraic division to find that(xx8)÷(x2)=x+2x+4so(xx8)=(x+2x+4)(x2)  =limx4(x+2x+4)(x2)(x2)(x+2) =limx4(x+2x+4)(x+2) =4+22+42+2=3

 

 

Here it the graph - it has a hole in it at (4,3)

https://www.desmos.com/calculator/3jmjqdwthb

 Jan 24, 2016
edited by Melody  Jan 24, 2016
edited by Melody  Jan 24, 2016
edited by Melody  Jan 24, 2016

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