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Old November 2nd, 2009, 05:22 PM
cpj cpj is offline
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Default Determine the limit and where possible compute.

hi, the problem i have is i'm having trouble with how to determine the limit using first principles, any help would be appreciated. the problem is..

lim (5x-2)^1/2 - 2(2^1/2)
x->2 (x^2)-(3x)+2

thanks for any help, i've never had much luck with limits
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Old November 2nd, 2009, 05:55 PM
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Originally Posted by cpj View Post
hi, the problem i have is i'm having trouble with how to determine the limit using first principles, any help would be appreciated. the problem is..

lim (5x-2)^1/2 - 2(2^1/2)
x->2 (x^2)-(3x)+2

thanks for any help, i've never had much luck with limits
Multiply numerator and denominator by the conjugate surd \sqrt{5x - 2} + \sqrt{8}, simplify the numerator, factorise the denominator, cancel the common factor and then take the limit. Please show your work if you need more help.
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Old November 3rd, 2009, 11:38 AM
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Default

(5x-2)^1/2 - (8)^1/2
x^2 - 3x + 2

[(5x-2)^1/2 - (8)^1/2] * [(5x-2)^1/2 + (8)^1/2]
[(5x-2)^1/2 + (8)^1/2]*[(x^2)-3x+2]


(5x-2)-8
[(5x-2)^1/2 + (8)^1/2]*(x-1)(x-2)


5
-2(2^1/2)

this is my final limit, could you tell me if its correct please. i'm not sure..
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Old November 3rd, 2009, 11:45 PM
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Originally Posted by cpj View Post
(5x-2)^1/2 - (8)^1/2
x^2 - 3x + 2

[(5x-2)^1/2 - (8)^1/2] * [(5x-2)^1/2 + (8)^1/2]
[(5x-2)^1/2 + (8)^1/2]*[(x^2)-3x+2]


(5x-2)-8
[(5x-2)^1/2 + (8)^1/2]*(x-1)(x-2)


5
-2(2^1/2)

this is my final limit, could you tell me if its correct please. i'm not sure..
I get \frac{5}{2 \sqrt{8}}.
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