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  • 設(shè)空間兩個(gè)單位向量向量OA=(m,n,0),向量OB=(0,n,p)與向量OC=(1,1,1)的夾角都等于π/4,

    設(shè)空間兩個(gè)單位向量向量OA=(m,n,0),向量OB=(0,n,p)與向量OC=(1,1,1)的夾角都等于π/4,
    數(shù)學(xué)人氣:726 ℃時(shí)間:2020-10-01 10:30:29
    優(yōu)質(zhì)解答
    |OA|=1
    => m^2+n^2 = 1(1)
    OA.OC = |OA||OC|cos(π/4)
    (m,n,0).(1,1,1) = 1. √3 ( √2/2)
    m+n = √6/2(2)
    sub (2) into (1)
    m^2 +(√6/2-m)^2 =1
    4m^2 - 2√6m + 1 =0
    m = (√6 +√2)/4 or(√6 -√2)/4
    when m= (√6 +√2)/4 , n= (√6 -√2)/4
    when m= (√6 -√2)/4 , n= (√6 +√2)/4

    OA = ((√6 +√2)/4 , (√6 -√2)/4, 0)or((√6 -√2)/4 ,(√6 +√2)/4,0)
    Similarly,
    OB.OC = |OB||OC|cos(π/4)
    (0,n,p). (1,1,1) = 1. √3 (√2/2)
    n+p = √6/2
    p =√6/2 - n
    when n = (√6 -√2)/4, p=(√6 +√2)/4
    when n = (√6 +√2)/4, p=(√6 -√2)/4
    OB =(0, (√6 -√2)/4, (√6 +√2)/4) or(0, (√6 +√2)/4, (√6 -√2)/4)
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