Saturday, November 1, 2014

Evaluate the limit of y=(2x^2-x-3)/(x+1), x-->-1 using L'Hopital theorem.

We'll verify if the limit exists, for x =
-1.


We'll substitute x by -1 in the expression of the
function.


lim y = lim
(2x^2-x-3)/(x+1)


lim (2x^2-x-3)/(x+1) =  (2+1-3)/(-1+1) =
0/0


We've get an indetermination
case.


We could solve the problem in 2 ways, at
least.


We'll apply L'Hospital
rule:


lim f(x)/g(x) = lim
f'(x)/g'(x)


f(x) = 2x^2-x-3 => f'(x) =
4x-1


g(x) = x+1 => g'(x) =
1


lim (2x^2-x-3)/(x+1) = lim
(4x-1)


lim (2x^2-x-3)/(x+1) = 4*(-1) - 1 =
-5

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