maths help required

[tarquin008]

need help on this question:

the position of an objectat any time , t , is given as follows r(t): 3t²i + t³j - 6tk
find when the object is moving in a direction parallel to the unit vector k

any help much appreciated

[shinny]

Uhh, perhaps I've misunderstood the question/theory, but for some reason I'm getting for no values of t will the particle be moving parallel to k. Anyone got any ideas? Or is that the actual answer...

[bigtick]

At t =0.

[Collin Li]

Differentiate the position vector with respect to t to get your velocity vector. Find t such that the i and j components are zero (and k non-zero). The answer is t = 0.

[tarquin008]

a complex number question i need help on .... i know, i suck at maths

if z= x + yi, find the values of x and y such that ( z - 1) divided by ( z + 1 ) = i

[shinny]

Given the simplicity of the answer, there might be a much faster way of approaching this but meh =T

[Collin Li]

Equating real and imaginary parts:

    --(1)

                             --(2)

Equating them:

[tarquin008]

yeah thanks

[Mao]

there's some major confusion with + and - there


corrected version:

[shinny]

Whoops, confused it near the start of transcribing and I thought I fixed it back up. Guess not =T