How do you use the epsilon delta definition to prove that the limit of #x/(6-x)=1# as #x->3#?

Answer 1

We can prove that

#abs (f(x) - 1) < epsilon # for #abs (x-3) < delta_epsilon#

if #delta_epsilon = (3epsilon)/(2-epsilon)#

This would not be necessary as:

#f(x) = x/(6-x)#
is continuous in #x=3#, so:
#lim_(x->3) f(x) = f(3) = 3/(6-3) = 3/3 =1#

However, as an exercise, we can see that:

#abs (f(x) - 1) = abs ( x/(6-x) -1 )= abs ( (x-6+x)/(6-x) )= abs (2x-6) / abs (6-x)#
Now consider #x in (3-delta, 3+delta)# with # delta > 0# so that:
#abs (x-3) < delta#.

We have:

#abs(6-x) = abs (3 +3-x) <= abs(3) + abs (3-x) < 3+delta#

and

#abs (2x-6) = abs (2(x-3)) = 2 abs(x-3) < 2delta#

Putting this two inequalities together:

#abs (f(x) - 1) < (2delta)/(3+delta)#
This means that given #epsilon < 0# if we choose #delta_epsilon# such that:
#epsilon = (2delta_epsilon)/(3+delta_epsilon)#

that is:

#delta_epsilon = (3epsilon)/(2-epsilon)#

we will have:

#abs (f(x) - 1) < epsilon # for #abs (x-3) < delta_epsilon#
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Answer 2

To prove that the limit of x/(6-x) is 1 as x approaches 3 using the epsilon-delta definition, we need to show that for any given epsilon greater than 0, there exists a delta greater than 0 such that if 0 < |x - 3| < delta, then |x/(6-x) - 1| < epsilon.

Let's begin the proof:

Given epsilon > 0, we need to find a suitable delta > 0.

|x/(6-x) - 1| = |x - 6 + x| / |6 - x| = |2x - 6| / |6 - x|

To simplify further, we can assume that delta < 1, which implies 2 < x < 4.

Now, let's consider |2x - 6| / |6 - x| < epsilon.

Since 2 < x < 4, we can say that 0 < 6 - x < 2.

Therefore, |2x - 6| / |6 - x| < |2x - 6| / 2.

To ensure that |2x - 6| / 2 < epsilon, we can set |2x - 6| < 2epsilon.

Now, we can choose delta = min{1, 2epsilon}.

If 0 < |x - 3| < delta, then it implies that 2 < x < 4 and |2x - 6| < 2epsilon.

Hence, |x/(6-x) - 1| = |2x - 6| / |6 - x| < |2x - 6| / 2 < 2epsilon / 2 = epsilon.

Therefore, we have shown that for any epsilon > 0, there exists a delta > 0 such that if 0 < |x - 3| < delta, then |x/(6-x) - 1| < epsilon.

Hence, the limit of x/(6-x) as x approaches 3 is indeed 1.

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Answer from HIX Tutor

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

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