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Answers for “为什么 f(0) 等于 1?”

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To evaluate the right-hand limit (lim⁡x→c+f(x)\lim_{x \to c^+} f(x)), trace the graph starting from x-values greater than c and moving leftward toward c. Observe the height (y-value) that the curve approaches.

Conditions: Evaluating the limit from the right side (inputs strictly greater than c).; The graph shows a clear trend toward a finite y-level.

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Because the recursive formula needs a previous forecast, the video demonstrates a simple initialization method: set the first forecast equal to the first actual observation. In the example this gives F(1)=A(1)=1103F(1)=A(1)=1103.

Conditions: Applies when no earlier forecast is available.; Shown specifically for Week 1 in the example.

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The volume under a surface z=f(x,y)z=f(x,y) over a rectangular region [a,b]×[c,d][a,b] \times [c,d] is defined through a four-step limiting process using double Riemann sums. First, the region is partitioned into subrectangles with area ΔAk=ΔxkΔyk\Delta A_k = \Delta x_k \Delta y_k, and a sample point (xk,yk)(x_k,y_k) is chosen in each. The volume is approximated by the sum ∑k=1nf(xk,yk)ΔxkΔyk\sum_{k=1}^n f(x_k,y_k) \Delta x_k \Delta y_k, and the exact volume is defined as the limit of this sum as the partition norm ∥P∥→0\|P\| \to 0.

Conditions: The base region must be a rectangle [a,b]×[c,d][a,b] \times [c,d].; The function f(x,y)f(x,y) defines the height of the surface.; The limit is taken as the largest subrectangle area approaches zero.

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To draw the graph of a continuous uniform distribution, plot the lower bound 'a' and the upper bound 'b' on the horizontal x-axis. Then, plot the constant probability density value 1b−a\frac{1}{b-a} on the vertical y-axis.

Conditions: You know the values of the lower bound a and the upper bound b.; You have calculated the constant probability density value 1b−a\frac{1}{b-a}.

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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).

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After substituting t=0t=0 and F(ω)=2sin⁡ωωF(\omega) = 2 \frac{\sin \omega}{\omega} into the inverse Fourier transform formula, the equation becomes 1=12π∫−∞∞2sin⁡ωωdω1 = \frac{1}{2\pi} \int_{-\infty}^{\infty} 2 \frac{\sin \omega}{\omega} d\omega. The constant 2 in the numerator of the integrand cancels with the constant 2 in the denominator of the prefactor 12π\frac{1}{2\pi}.

Conditions: The inverse Fourier transform formula is used: f(0)=12π∫−∞∞F(ω)dωf(0) = \frac{1}{2\pi} \int_{-\infty}^{\infty} F(\omega) d\omega.; f(0)=1f(0) = 1.; F(ω)=2sin⁡ωωF(\omega) = 2 \frac{\sin \omega}{\omega}.

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To calculate exponential smoothing forecasts step-by-step, first initialize the first forecast equal to the first actual demand. Then, for each subsequent period, substitute the previous period's actual demand and previous forecast into the formula Ft+1=αAt+(1−α)FtF_{t+1} = \alpha A_t + (1-\alpha)F_t to compute the next forecast, repeating this recursive process until the target period is reached.

Conditions: The smoothing constant α\alpha is fixed across all periods.; An initial forecast F1F_1 is established from A1A_1.; Each new forecast depends only on the immediately preceding actual demand and forecast.

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Once the full derivative curve is available, you select any desired xx-coordinate within the visible window, look vertically up or down to intersect the orange parabolic graph, and interpret that exact vertical height as the slope of the tangent line to the original blue curve at that same xx.

Conditions: The derivative curve spans the continuous plotting area.; Requires recognizing that the vertical position of the derivative graph encodes slope, not just the function output of ff itself.

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The video demonstrates initializing the first forecast by setting it directly equal to the first period's actual demand. Because there is no prior forecast available to use in the recursive formula, the observed actual demand for period 1 is placed straight into the forecast column as F1F_1.

Conditions: Used when no prior forecast is available.; Applied specifically to period 1 in this example.; After initialization, later forecasts are generated recursively starting from period 2.