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Year 12s: what will be the first way you research your future options? >>

Year 12s: what will be the first way you research your future options? >>

AS Further Maths

I don't get how to do this, I get why i.j = j.k = k.i = 0 but I don't get how I use that to solve it
https://imgur.com/gallery/iguHGoq
Thanks for any help

(edited 5 years ago)

Study Forum Helper

Original post by jackwhurt

I don't get how to do this, I get why i.j = j.k = k.i = 0 but I don't get how I use that to solve it
https://imgur.com/gallery/iguHGoq
Thanks for any help

\mathbf{a} \cdot \mathbf{b} = (a_1 \mathbf{i} + b_1 \mathbf{j} + c_1 \mathbf{k})(a_2 \mathbf{i} + b_2 \mathbf{j} + c_2 \mathbf{k})

Now expand the two brackets and use that fact.

OP

Original post by RDKGames

\mathbf{a} \cdot \mathbf{b} = (a_1 \mathbf{i} + b_1 \mathbf{j} + c_1 \mathbf{k})(a_2 \mathbf{i} + b_2 \mathbf{j} + c_2 \mathbf{k})

Now expand the two brackets and use that fact.

where am i getting a3 and b3 from?

Study Forum Helper

Original post by jackwhurt

where am i getting a3 and b3 from?

Yeah just noticed... they meant:

\mathbf{a} = a_1 \mathbf{i} + a_2 \mathbf{j} + a_3 \mathbf{k}

\mathbf{b} = b_1 \mathbf{i} + b_2 \mathbf{j} + b_3 \mathbf{k}

OP

Original post by RDKGames

Yeah just noticed... they meant:

\mathbf{a} = a_1 \mathbf{i} + a_2 \mathbf{j} + a_3 \mathbf{k}

\mathbf{b} = b_1 \mathbf{i} + b_2 \mathbf{j} + b_3 \mathbf{k}

Alright, thanks mate

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