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麻煩請各大大幫我,給我計算過程!!!
設線段PQ=11,若線段PQ在x軸之正射影長為8,在y軸之正射影長為3,則在z軸之正射影長為多少？ (正解：四分之根號三)?
設 P = (0,0,0); Q = (x,y,z) = (8,3,z); 則 PQ^2 = 121 = 64 + 9 + z^2 z^2 = 121 - 73 = 48 z = +- 4√3 課本答案錯誤
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https://tw.answers.yahoo.com/question/index?qid=20150823022005AAey0U3