AS Further Maths Watch

jackwhurt
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#1
Report Thread starter 6 days ago
#1
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
Last edited by jackwhurt; 6 days ago
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RDKGames
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#2
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(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.
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jackwhurt
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#3
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(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?
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RDKGames
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(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}
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jackwhurt
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(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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