Parrallel vectors

[sajib_mostofa]

Q. Given , and , the values for m and n for which u + w is parrellel to v are?

[kakar0t]

does m=-2 and n=-1

if they do i'll scan my working

if it doesn't, then dw lol

[sajib_mostofa]

Yeah it does

[moekamo]

to be parallel to v, where is a constant

so ,

equating i, j, k components, ,



and

so answer is n=-1 and m=-2 like kakar0t said

[kakar0t]

Sorry for the bad quality, scanner doesn't pick up pencil well.

If you need me to clarify things please ask.

(same as moekamos clear, precise explanation)

[sajib_mostofa]

Thanks to both of you. But why don't I get the same answer when using dot product and making ?

[m@tty]

That is only true if both vectors are unit vectors. (Or if the product of their magnitudes equals 1)

Because if they are parallel, then the angel between them is zero.

Hence,

[sajib_mostofa]

ahh I was unaware of that. cheers Matty

[Martoman]

to be parallel to v, where is a constant

so ,

equating i, j, k components, ,



and




so answer is n=-1 and m=-2 like kakar0t said

This is the best way.

To do it quickly and sneakily, realise that the scale factor difference in the K term is 2. That then means that all components are the same except for a factor of 2... essentially what moekamo said.

[sajib_mostofa]

to be parallel to v, where is a constant

so ,

equating i, j, k components, ,



and




so answer is n=-1 and m=-2 like kakar0t said

This is the best way.

To do it quickly and sneakily, realise that the scale factor difference in the K term is 2. That then means that all components are the same except for a factor of 2... essentially what moekamo said.

So you don't recommend using dot product?

[Martoman]

No because this way you get the answer in about 3 lines without considering the pitfalls matty detailed. Save you confusing yourself and just go for the simplest method.