Question
Show that 10000x^2 is O(x^3) but x^3 is not O(10000x^2)
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Answer to a math question Show that 10000x^2 is O(x^3) but x^3 is not O(10000x^2)
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4.5110 Answers
1. To show \(10000x^2\) is \(O(x^3)\):
f(x) = 10000x^2
g(x) = x^3
Find \(C\) and \(k\) such that for all \(x > k\),
10000x^2 \leq Cx^3
\frac{10000}{x} \leq C
As \(x \to \infty\), \(\frac{10000}{x} \to 0\). Choose \(C = 10000\) and \(k = 1\). Thus,
10000x^2 \text { is } O(x^3).
2. To show \(x^3\) is not \(O(10000x^2)\):
f(x) = x^3
g(x) = 10000x^2
If \(x^3\) were \(O(10000x^2)\), for some \(C\) and \(k\),
x^3 \leq C \cdot 10000x^2
\frac{x}{10000} \leq C
As \(x \to \infty\), \(x\) cannot be bounded by a constant \(10000C\). Thus,
x^3 \text { is not } O(10000x^2).
Final answer:
10000x^2 \text { is } O(x^3) \text { but } x^3 \text { is not } O(10000x^2)
Find \(C\) and \(k\) such that for all \(x > k\),
As \(x \to \infty\), \(\frac{10000}{x} \to 0\). Choose \(C = 10000\) and \(k = 1\). Thus,
2. To show \(x^3\) is not \(O(10000x^2)\):
If \(x^3\) were \(O(10000x^2)\), for some \(C\) and \(k\),
As \(x \to \infty\), \(x\) cannot be bounded by a constant \(10000C\). Thus,
Final answer:
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