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Answers for “y=(7,6) 在 u=(2,1) 上的投影是什么?”

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Find a method

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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)

Find a method

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First, find the residual by subtracting the projection (8,4)(8,4) from y=(7,6)y=(7,6), resulting in (−1,2)(-1,2). Then, compute the dot product of the projection (8,4)(8,4) and the residual (−1,2)(-1,2).

Conditions: y=(7,6)y = (7,6); Projection is (8,4)(8,4); Residual is (−1,2)(-1,2)

Understand why

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The residual vector is defined as yy minus its projection onto the line spanned by vv. By the geometric definition of orthogonal projection, the difference between a vector and its projection onto a subspace is orthogonal to that subspace.

Conditions: vv is a nonzero vector.; The projection is orthogonal.

Meet the concept

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The orthogonal projection of yy onto the line spanned by a nonzero vector vv is given by the formula y⋅vv⋅vv\frac{y \cdot v}{v \cdot v} v. This formula scales the vector vv by the ratio of the dot product of yy and vv to the dot product of vv with itself.

Conditions: The vector vv must be nonzero.; The projection is onto the line spanned by vv.