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How would i find these vectors? I have no idea!?

For u=(26,6,−21) and v=(−18,−6,12), find the vectors u1 and u2 such that:

(i) u1 is parallel to v

(ii) u2 is orthogonal to v

(iii) u = u1 + u2

1 Answer

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  • 1 decade ago
    Favorite Answer

    Any vector that is scalar multiple of v would be parallel to v

    ie. k( -18, -6, 12 ) is parallel to v where k is any real number.

    u1 = (-18k, -6k, 12k)

    u2 is orthogonal to v. Say let u2 be (a, b, c)

    u2. v = 0

    -18a-6b+12c = 0

    -3a-b+2c=0

    b=-3a+2c

    since u = u1+u2

    -18k+a = 26

    -6k+b = 6

    12k+c = -21

    but b = -3a+2c

    thus the 3 equations

    -18k + a = 26

    -6k -3a + 2c = 6

    12k + c = -21

    solving k = -1.5, a = -1 c = -3, b = -3

    u1= (27, 9, -18)

    u2= (-1,-3,-3)

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