CHAPTER 1 LIMITS
SECTION 1.3 Limit Theorems
Problem Set 1.3, Number 25 – 51.
- lim√[ f2(x) + g2(x)]x → a
- lim2f(x) – 3g(x)x → af(x) + g(x)
- lim∛(g(x)) ⋅ [f(x) + 3]x → a
- lim[f(x) – 3]⁴x → a
- lim[ |f(t)) + |3g(t)| ]t → a
- lim[f(u) + 3g(u)]3u → a
- f(x)=3x2
- f(x)=3x2 + 2x + 1
- f(x)=1x
- f(x)=3x2
- Prove Statement 6 of Theorem A. Hint:
- Prove Statement 7 of Theorem A by first giving an ε – δ proof that limx→c [1/g(x)] = 1/[limx→c g(x)] and then applying Statement 6.
- Prove that limx→c f(x) = L ⇔ limx→c [f(x) – L] = 0.
- Proof that limx→c f(x) = 0 ⇔ limx→c |f(x)| = 0.
- Proof that limx→c |x| = |c|.
- Find examples to show that if
- lim√(3 + x)x → –3+x
- lim√(π3 + x3)x → –π+x
- limx – 3x → –3+√(x2 – 9)
- lim√(1 + x)x → 1–4 + 4x
- lim(x2 + 1) 〚x〛x → 2+(3x – 1)2
- lim(x – 〚x〛)x → 3–
- limxx → 0–|x|
- Lim〚x2 + 2x〛x → 3+
- Suppose that f(x)g(x) = 1 for all x and limx→a g(x) = 0. Prove that limx→a f(x) does not exist.
- Let R be the rectangle joining the midpoint of the sides of the quadrilateral Q having vertices (±x, 0) and (0, ±1). Calculate.
- Let y = √x and consider the point M, N, O, and P with coordinates (1, 0), (0, 1), (0, 0), and (x, y) on the graph of y = √x, respectively. Calculate
In Problems 25-30, find the limits if limx→a f(x) = 3 and limx→a g(x) = –1 (see Example 4).
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BACA JUGA:
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In Problems 31-34, find limx→2 [f(x) – f(2)] / (x – 2) for each given function f.
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PEMBAHASAN:
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|f(x)
g(x) – LM
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=
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|f(x)
g(x) – Lg(x) + Lg(x) – LM
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=
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|g(x)
[f(x) – L] + L [g(x) – M]|
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≤
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|g(x)|
|f(x) – L| + |L| |g(x) – M|
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Now show that if limx→c g(x) = M, then there is a number δ1 such that
0 < |x – c| < δ1 ⇒ |g(x)| < |M| + 1
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PEMBAHASAN:
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Suppose limx→c f(x) = L and limx→c g(x) = M.
|f(x) g(x) – LM| ≤ |g(x)||f(x) – L| + |L||g(x) – M| as shown in the text.
Choose ε1 = 1.
Since limx→c g(x) = M, there is some δ1 > 0 such that if 0 < |x – c| < δ1, |g(x) – M| < ε1 = 1 or M – 1 < g(x) < M + 1.
|M – 1| ≤ |M| + 1 and |M + 1| ≤ |M| + 1 so for 0 < |x – c| < δ1, |g(x)| < |M| + 1.
Choose ε > 0.
Since limx→c f(x) = L and limx→c g(x) = M, there exist δ2 and δ3 such that 0 < |x – c| < δ2 ⇒ |f(x) – L| < ε / (|L| + |M| + 1) and 0 < |x – c| < δ3 ⇒ |g(x) – M| < ε / (|L| + |M| + 1).
Let δ = min {δ1, δ2, δ3}, then 0 < |x – c| < δ ⇒ |f(x) g(x) – LM| ≤ |g(x)||f(x) – L| + |L||g(x) – M| < (|M| + 1) ε / (|L| + |M| + 1) + |L| ε / (|L| + |M| + 1) = ε.
Hence,
limx→c f(x)g(x) = LM = (limx→c f(x))(limx→c g(x))
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PEMBAHASAN:
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Say limx→c g(x) = M, M ≠ 0, and choose ε1 = ½|M|.
There is some δ1 > 0 such that
0 < |x – c| < δ1 ⇒ |g(x) – M| < ε = ½|M| or M – ½|M| < g(x) < M + ½|M|.
|M – ½|M|| ≥ |½|M|| and |M + ½|M|| ≥ |½|M|| so |g(x)| > ½|M| and 1/|g(x)| < 2/|M|.
Choose ε > 0.
Since limx→c g(x) = M there is δ2 > 0 such that
0 < |x – c| < δ2 ⇒ |g(x) – M| < ½M2.
Let δ = min {δ1, δ2, then
0 < |x – c| < δ ⇒ |1/g(x) – 1/M|
= |M – g(x)/g(x)M|
= 1/|M||g(x)| ⋅ |g(x) – M| < 2/M2 ⋅ |g(x) – M|
= 2/M2 ⋅ ½M2ε
= ε
Thus, limx→c 1/g(x) = 1/M = 1/ limx→c g(x).
Using statement 6 and the above result,
limx→c f(x)/g(x) = limx→c f(x) ⋅ limx→c 1/g(x) = limx→c f(x) ⋅ 1/ limx→c g(x) = limx→c f(x)/limx→c g(x).
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BACA JUGA:
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(a)
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limx
→ c [f(x) + g(x)] exists, this does not imply that either limx
→ c f(x) or limx → c
g(x) exists;
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(b)
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limx
→ c [f(x) ⋅ g(x)] exists, this does not imply that
either limx → c f(x) or limx
→ c g(x) exists.
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PEMBAHASAN:
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a.
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If f(x)
= (x + 1)/(x – 2), g(x) = (x
– 5)/(x – 2) and c = 2, then limx
→ c [f(x) + g(x)] exists, but neither limx → c
f(x) nor limx → c g(x)] exists.
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b.
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If f(x)
= 2/x, g(x) = x and c
= 0, then limx → c [f(x) + g(x)] exists, but neither limx
→ c f(x) does not exists.
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PEMBAHASAN:
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PEMBAHASAN:
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BACA JUGA:
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PEMBAHASAN:
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PEMBAHASAN:
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PEMBAHASAN:
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PEMBAHASAN:
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lim
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perimeter
of R
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x → 0+
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perimeter
of Q
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PEMBAHASAN:
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(a)
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lim
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perimeter
of ∆ NOP
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x → 0+
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perimeter
of ∆ MOP
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PEMBAHASAN:
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(b)
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lim
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area
of ∆ NOP
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x → 0+
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area
of ∆ MOP
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PEMBAHASAN:
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BACA JUGA:
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