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Given AB = -i + 3j and AC = 4i − 5j. Find BC. Also, if the positional vector of point A is u and the positional vector of point B is v, find vector AB in terms of u and v.

Mathematics

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Answers

2 parts
4

5i - 8j

5

v - u

Step-by-step solution

6 steps

Here are the solutions to Questions 4 and 5.

Part 4· 3 steps

Given AB⃗=−i+3j\vec{AB} = -i + 3j and AC⃗=4i−5j\vec{AC} = 4i - 5j.
Find BC⃗\vec{BC}.

  1. Express BC⃗\vec{BC} in terms of the given vectors.

    We can use the triangle law of vector addition. To go from B to C, we can go from B to A, and then from A to C.

    BC⃗=BA⃗+AC⃗\vec{BC} = \vec{BA} + \vec{AC}
  2. Find BA⃗\vec{BA} from AB⃗\vec{AB}.

    The vector BA⃗\vec{BA} is the negative of AB⃗\vec{AB}.

    BA⃗=−AB⃗=−(−i+3j)=i−3j\vec{BA} = -\vec{AB} = -(-i + 3j) = i - 3j
  3. Substitute the vectors into the expression for BC⃗\vec{BC} and calculate.

    BC⃗=(i−3j)+(4i−5j)\vec{BC} = (i - 3j) + (4i - 5j) BC⃗=(1+4)i+(−3−5)j\vec{BC} = (1+4)i + (-3-5)j BC⃗=5i−8j\vec{BC} = 5i - 8j

    The vector BC⃗\vec{BC} is:

    5i−8j\boxed{5i - 8j}

Part 5v - u

The positional vector of point A is uu and the positional vector of point B is vv.
Find vector AB⃗\vec{AB} in terms of uu and vv.

  1. Understand positional vectors.

    The positional vector of point A, uu, means OA⃗=u\vec{OA} = u.
    The positional vector of point B, vv, means OB⃗=v\vec{OB} = v.

  2. Express AB⃗\vec{AB} using positional vectors.

    To find the vector from point A to point B, we subtract the positional vector of the starting point (A) from the positional vector of the ending point (B).

    AB⃗=OB⃗−OA⃗\vec{AB} = \vec{OB} - \vec{OA}
  3. Substitute the given positional vectors.

    AB⃗=v−u\vec{AB} = v - u

    The vector AB⃗\vec{AB} in terms of uu and vv is:

    v−u\boxed{v - u}
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