Prove the following limit.\lim 5x-4=6x\rightarrow2Z

sfair24bz

sfair24bz

Answered question

2021-11-19

Prove the following limit.
lim5x4=6
x2
SOLUTION 1. Preliminary analysis of the problem guessing a value for δ Let € be a given positive number.
We want to find a number δ such that
if 0∣<x2∣<δ then(5x4)6∣<ϵ.
But (5x4)6∣=∣5x10∣=5||. Therefore, we want δ
if 0<∣x2∣<δ then5∣∣ <ϵ
such that
that is, if 0<∣x2∣<δ then∣∣<ϵϵ5
This suggests that we should choose δ=ϵ/5.
2. Proof (showing that δ works). Given ϵ>0, choose δ= 
ϵ/5.If 0<∣∣<δ, then
(5x4)6∣=∣∣
=5∣∣<5δ
=5()
=ϵ
Thus
if 0<∣x2∣<δ then(5x4)6∣<ϵ.
Therefore, by the definition of a limit
lim5x4=6
x2

Answer & Explanation

Roger Noah

Roger Noah

Beginner2021-11-20Added 17 answers

Given,
lim5x4=6
x2
Let ϵ be a given positive number.
We want to find a number δ such that,
if 0<∣x2∣<δ then (5x4)6∣<ϵ.
But
(5x4)6∣=∣5x10
=∣5(x2)
=5x2
Therefore we want δ such that
if 0<∣x2∣<δ then 5x2∣<ϵ.
That is,
if 0<∣x2∣<δ thenx2∣<ϵ5.
This suggests that we should choose δ=ϵ5
Step 2
Given ϵ>0, choose δ=ϵ5.
if 0<∣x2∣<δ, then
(5x4)6∣=∣5x10
=5x2∣<5δ
=5(x2∣<δ)
=5(ϵ5)
=ϵ
Thus,
if 0<∣x2∣<δ then(5x4)6∣<ϵ
Therefore by the definition of a limit,
lim(5x4)=6
x2

Step 2
Given ϵ>0, choose δ=ϵ5.
if 0<∣x2∣<δ, then
(5x4)6∣=∣5x10
=5x2∣<5δ
=5(x2∣<δ)
=5(ϵ5)
=ϵ
Thus,
if 0<∣x2∣<δ then(5x4)6∣<ϵ.
Therefore by the definition of a limit,
lim(5x4)=6
x2

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