Length of a projection

Let b=(4,3)b=(4,3) and let LL be the line through the origin in the direction a=(2,1)a=(2,1). Project bb orthogonally onto LL. What is the length of that projection vector? Give a decimal to four places.

Show hints (2)+
  1. Projection length onto aa is aba\dfrac{a\cdot b}{\|a\|}.
  2. ab=11a\cdot b=11, a=5\|a\|=\sqrt5.

Answer

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4.9193 (± 0.001)

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Asked at: Game-Based Aptitude, ETF Market-Making

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