Consider the function f(x) = x3 for x ∈ ℝ and –2 < x < 4. Prove that limx→1 f(x) = 1

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ISBN:9780470458365
Author:Erwin Kreyszig
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Chapter2: Second-order Linear Odes
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Consider the function f(x) = x3 for x ∈ ℝ and –2 < x < 4. Prove that limx→1 f(x) = 1. Use the method shown in Example 3.7.5. (I attached Example 3.7.5 files)

2x2-5x-3
Vx (0 < x - 3|< 8 →
x-3
-7| <e).
The scratch work involved in finding 8 will not appear in the proof, of course.
In the final proof we'll just write "Let 8 = (some positive number)" and then
proceed to prove
Vx
(0 < x - 3|< 8 →
|2x2-5x-3
x-3
3 -7| < €).
Before working out the value of 8, let's figure out what the rest of the proof
will look like. Based on the form of the goal at this point, we should proceed
by letting x be arbitrary, assuming 0 < |x − 3] < 8, and then proving | (2x² -
5x-3)/(x-3)-7| < €. Thus, the entire proof will have the following form:
Let € be an arbitrary positive number.
Let 8 = (some positive number).
Let x be arbitrary.
Suppose 0 < x— 3| < 8.
-
[Proof of | (2x2-5x-3)/(x-3) - 7| < € goes here.]
-
Therefore 0 < x - 3|<8 → |(2x² - 5x-3)/(x-3)-7| < €.
Since x was arbitrary, we can conclude that Vx(0 < |x − 3] < 8 →
|(2x2-5x-3)/(x − 3) — 7| < €).
-
-
Therefore 380Vx(0 < |x −3] < 8 → |(2x²-5x-3)/(x-3)−7| < €).
Since & was arbitrary, it follows that Ve > 0380Vx (0 < |x − 3] < 8 →
| (2x2-5x-3)/(x − 3) — 7| < €).
-
-
-
Transcribed Image Text:2x2-5x-3 Vx (0 < x - 3|< 8 → x-3 -7| <e). The scratch work involved in finding 8 will not appear in the proof, of course. In the final proof we'll just write "Let 8 = (some positive number)" and then proceed to prove Vx (0 < x - 3|< 8 → |2x2-5x-3 x-3 3 -7| < €). Before working out the value of 8, let's figure out what the rest of the proof will look like. Based on the form of the goal at this point, we should proceed by letting x be arbitrary, assuming 0 < |x − 3] < 8, and then proving | (2x² - 5x-3)/(x-3)-7| < €. Thus, the entire proof will have the following form: Let € be an arbitrary positive number. Let 8 = (some positive number). Let x be arbitrary. Suppose 0 < x— 3| < 8. - [Proof of | (2x2-5x-3)/(x-3) - 7| < € goes here.] - Therefore 0 < x - 3|<8 → |(2x² - 5x-3)/(x-3)-7| < €. Since x was arbitrary, we can conclude that Vx(0 < |x − 3] < 8 → |(2x2-5x-3)/(x − 3) — 7| < €). - - Therefore 380Vx(0 < |x −3] < 8 → |(2x²-5x-3)/(x-3)−7| < €). Since & was arbitrary, it follows that Ve > 0380Vx (0 < |x − 3] < 8 → | (2x2-5x-3)/(x − 3) — 7| < €). - - -
Example 3.7.5. Show that
2x2-5x-3
lim
x→3 x-3
= 7.
Scratch work
According to the definition of limits, our goal means that for every positive
number € there is a positive number 8 such that if x is any number such that
0<|x3|< 8, then | (2x² -5x-3)/(x-3) - 7| < €. Translating this into
logical symbols, we have
Ve>0x0<
2x2-5x-3
-31 < 8→
x-3
기).
< E
We therefore start by letting & be an arbitrary positive number and then try to
find a positive number 8 for which we can prove
Vx0<|x3| < 8 →
|2x2-5x-3
x-3
-7|<e).
The scratch work involved in finding 8 will not appear in the proof, of course.
In the final proof we'll just write "Let 8 = (some positive number)" and then
proceed to prove
Vx
5/2r2-5x-3
-7|<e).
<€).
(0 < x - 3|< 8 →
Before working out the value of 8, let's figure out what the rest of the proof
will look like. Based on the form of the goal at this point, we should proceed
by letting x be arbitrary, assuming 0 < |x − 3] < 8, and then proving | (2x² -
5x-3)/(x-3)-7] < €. Thus, the entire proof will have the following form:
Let € be an arbitrary positive number.
Previous
Transcribed Image Text:Example 3.7.5. Show that 2x2-5x-3 lim x→3 x-3 = 7. Scratch work According to the definition of limits, our goal means that for every positive number € there is a positive number 8 such that if x is any number such that 0<|x3|< 8, then | (2x² -5x-3)/(x-3) - 7| < €. Translating this into logical symbols, we have Ve>0x0< 2x2-5x-3 -31 < 8→ x-3 기). < E We therefore start by letting & be an arbitrary positive number and then try to find a positive number 8 for which we can prove Vx0<|x3| < 8 → |2x2-5x-3 x-3 -7|<e). The scratch work involved in finding 8 will not appear in the proof, of course. In the final proof we'll just write "Let 8 = (some positive number)" and then proceed to prove Vx 5/2r2-5x-3 -7|<e). <€). (0 < x - 3|< 8 → Before working out the value of 8, let's figure out what the rest of the proof will look like. Based on the form of the goal at this point, we should proceed by letting x be arbitrary, assuming 0 < |x − 3] < 8, and then proving | (2x² - 5x-3)/(x-3)-7] < €. Thus, the entire proof will have the following form: Let € be an arbitrary positive number. Previous
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