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C4 Vectors

Haesights

Stuck on 21
I get AB= 2I +4j+6k
AP=0.75 of AB
so I get OP=4.5i+5j+3.5k

The answer is 6i+8j+8k

Where did I go wrong?

Reply 1

J10

let p=xi + yj +zk

then find AP and 3BP, and you'll have 3 equations to rearrange.

Reply 2

Haesights

Is there not an easier way?

Reply 3

ezioaudi77

Original post by Haesights

Is there not an easier way?

AP = 3BP (1)

AP = AB + BP (2)

Equate them to find BP, then OP = OB + BP.

Reply 4

the bear

if you draw a diagram you can see that the ratio of AB:BP is 2:1

this means that the changes in the x value from A to B and then B to P are in the same ratio... and the same for the y and z values

(edited 11 years ago)

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