Re: [中學] 矩陣、向量

[angel07 (Dark Moon Princess)]

※ 引述《dreamsletter (drmaticking)》之銘言：
: 如題
: 矩陣（填充2.）答案是3
: 向量（指考試題2.）答案是-7/8
: http://i.imgur.com/oaP4r4X.jpg
: http://i.imgur.com/8mgTo4d.jpg
: 我矩陣那裡是哪裡寫錯了嗎@@

[matrix]

A=A^(-1)

A*A^(-1)=A^2=I

a^2-8=1 (a>0)

a=3

[vector]

 |u|^2 = 4|v|^2 = |2u+3v|^2
=4|u|^2 + 12u．v + 9|v|^2
=25|v|^2 + 12u．v

u．v=(-7/4)|v|^2

cosθ=u．v/|u|*|v|=(-7/4)/(2*1)=-7/8


--
This card must attack if able. Other cards or effects cannot be activated
during either player's Battle Phase. Any effects of the monster which battles
with this card are negated. If an attack declaration involve this card:
destroy that monster, and if you do, inflict damage equal to its ATK or DEF
to your opponent. During End Phase, if this card didn't battle or activate
its effect this turn: destroy this card.

--
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推 dreamsletter: 謝謝您的解答！！ 那可以請問一下我原本那樣列為什
→ dreamsletter: 麼不行嗎@@ 是沒有用到題目的條件嗎
→ angel07     : 你矩陣那題根本符號搞錯 所以當然結果錯
→ angel07     : 向量那題就用|a+b|^2=|a|^2+2a．b+|b|^2來解
→ angel07     : 然後就是個純代數問題
→ dreamsletter: 喔喔了解我反矩陣列錯 謝謝大大！