Question 1202643
given that a=2i+3j-k, b=i-j+2k, and c=3i+4j+k, 
find a+2b-c
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<pre>
 2i + 6j - 1k ---- a
 2i - 2j + 4k ---- 2b
-3i - 4j - 1k ---- -c
-------------------------- Add
 1i + 0j + 2k
= i + 2k
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</pre>

(b) a vector d such that a+b+c+d=0
Add a, b and c
d = -1 * the sum
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and (c) a vector d such that a-b+c+3d=0
Add a, -b and c
d = (-1/3) time the sum