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Answers for “10.5 是如何得出的?”

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To find the left-hand limit as x approaches a value c (denoted lim⁡x→c−f(x)\lim_{x \to c^-} f(x)), observe the behavior of the function's curve strictly for input values less than c, moving towards c. If the y-values grow without bound in either the positive or negative direction, the finite real limit does not exist.

Conditions: The function has a vertical asymptote or discontinuity at x=cx=c.; You are evaluating the limit from the left side (inputs strictly less than c).

Understand why

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The bars represent the probabilities of all possible outcomes (head counts) for a fixed model. Because they exhaust the entire sample space, their sum must equal 1, which is the defining normalization property of a probability distribution.

Conditions: The coin model is fixed at p=0.5p=0.5.; The number of flips is 10.; kk indexes all possible head counts from 0 to 10.

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The video claims that, in this playground, the genetic algorithm can efficiently solve the Traveling Salesman Problem using the default parameters. The demo shows the route improving and the path length decreasing over iterations.

Conditions: The genetic-algorithm implementation is run with the displayed default parameters.; The problem instance is the one shown in the visualization.; The word "efficiently" is qualitative here; no formal efficiency metric or runtime bound is provided.

Understand why

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The decision rule is based on comparing the class average to a fixed threshold. An outlier artificially inflates the average above the threshold, preventing the class from receiving help.

Conditions: The decision rule is: hold extra classes only if the average score is below 35.; The dataset contains an outlier.; The threshold is fixed at 35.

Meet the concept

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It means that in the worst case, the algorithm's output cost is at most twice the true optimal cost.

Conditions: The problem is a minimization problem.; The algorithm is a 2-approximation.

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To compute the greatest common divisor of 1785 and 546, apply the Euclidean algorithm by repeatedly dividing the previous divisor by the previous remainder. Start with 1785 divided by 546.

Conditions: The inputs are 1785 and 546.; The Euclidean algorithm is used.; The division algorithm is applied at each step.

Meet the concept

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The probability density function (PDF) for a continuous uniform distribution on the interval [a, b] is a constant value given by the formula f(x)=1b−af(x) = \frac{1}{b - a}. The numerator 1 represents the total probability of 100%, while the denominator b−ab - a is the length of the interval, calculated as the upper bound minus the lower bound.

Conditions: The distribution is continuous and uniform.; The random variable is defined on the closed interval [a, b].; The lower bound a is strictly less than the upper bound b.

Understand why

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The expected number of heads is 50 because the expected value for a counting experiment like this is calculated as the number of trials multiplied by the probability of success on each trial. With 100 tosses and a fair coin (probability of heads = 0.5), the calculation is 100⋅0.5=50100 \cdot 0.5 = 50.

Conditions: The coin is fair.; There are 100 tosses per trial.; XX counts heads.

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A quadratic polynomial over a field is irreducible if and only if it has no roots in that field. You can check this by evaluating the polynomial at all elements of the field.

Conditions: The polynomial is of degree 2.; The coefficients are in a field.

Understand why

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The sample mean converges to 50 because 50 is the expected value E(X)E(X) of the random variable XX (number of heads in 100 fair-coin tosses). According to the law of large numbers, as the number of trials nn approaches infinity, the sample mean X‾n\overline{X}_n approaches the expected value.

Conditions: The coin is fair.; XX counts heads after 100 tosses.; nn approaches infinity.

Understand why

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The condition must hold for *every* ϵ>0\epsilon > 0 to ensure that f(x)f(x) can be made arbitrarily close to LL. If it only held for one specific ϵ\epsilon, the function values might be bounded within that range but not converge to LL.

Conditions: ϵ\epsilon represents an arbitrary positive tolerance.; The definition aims to prove convergence to a specific limit LL.

Understand why

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It is true because when 15 is divided by 12, the remainder is 3. This matches the definition of congruence modulo 12 used in the video.

Conditions: Use modulus 12.; Interpret the congruence via the remainder of division by 12.