Lim (2x-1)2-9 / x+1 x->-1 How to Evaluate the limit ?

Question

3179 views around the world

You can reuse this answer
Creative Commons License

Answer 1 · 2018-06-12T19:03:52

#-12#

#lim_(x->-1)((2x-1)^2-9)/(x+1)#

When we try to evaluate this directly we get:

#lim_(x->-1)((2x-1)^2-9)/(x+1)#

#=((2(-1)-1)^2-9)/((-1)+1)=((-3)^2-9)/(1-1)->0/0#

So the limit is indeterminate. A route to evaluating is by first expanding the bracket then simplifying the fraction like so:

#lim_(x->-1)((2x-1)^2-9)/(x+1)#

#=lim_(x->-1)(4x^2-4x+1-9)/(x+1)#

#=lim_(x->-1)(4x^2-4x-8)/(x+1)#

#=lim_(x->-1)(4(x^2-x-2))/(x+1)#

#=lim_(x->-1)(4(x+1)(x-2))/(x+1)#

#=lim_(x->-1)(4cancel((x+1))(x-2))/cancel(x+1)#

#=lim_(x->-1)4(x-2)=-12#