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Answers for “为什么系数是 2?”

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First, calculate the dot products y⋅u=20y \cdot u = 20 and u⋅u=5u \cdot u = 5. The scalar coefficient is 20/5=420/5 = 4.

Conditions: y=(7,6)y = (7,6); u=(2,1)u = (2,1)

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The coefficients are found sequentially by applying the three matching conditions at x=0x=0. First, substituting x=0x=0 into the polynomial and the function gives c0=1c_0=1.

Conditions: The approximation is centered at x=0x=0.; The target function is exe^x.; The approximating polynomial is c0+c1x+c2x2c_0+c_1x+c_2x^2.

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Treat the recurring integral as an algebraic variable (e.g., II). Move the term containing II from the right-hand side to the left-hand side by adding it to both sides.

Conditions: The integral II appears on both sides of the equation.; The coefficient of II on the right side is −1-1 (or another constant).; Algebraic manipulation is permitted.