141k views
1 vote
Find the scalar and vector projections of b onto a. a=⟨−5,12⟩, b=⟨4,6⟩

1 Answer

4 votes

Explanation:

The scalar projection of a vector b onto a vector a is given by the dot product of b and the unit vector of a:

p = (b · u) * u

where u is the unit vector of a, and can be found by dividing a by its magnitude:

u = a / ||a||

The vector projection of b onto a is simply the scalar projection scaled by the unit vector:

p = p * u

For the given vectors a = ⟨-5,12⟩ and b = ⟨4,6⟩, we first find the unit vector u:

u = a / ||a|| = ⟨-5,12⟩ / ||⟨-5,12⟩|| = ⟨-5/13,12/13⟩

Next, we find the dot product of b and u:

p = (b · u) = ⟨4,6⟩ · ⟨-5/13,12/13⟩ = (4 * -5/13) + (6 * 12/13) = -20/13 + 72/13 = 52/13

So the scalar projection of b onto a is p = 52/13.

Finally, we find the vector projection by scaling the unit vector u by the scalar projection:

p = p * u = (52/13) * ⟨-5/13,12/13⟩ = ⟨-52/169,104/169⟩

So the vector projection of b onto a is p = ⟨-52/169,104/169⟩.

User Camino
by
6.8k points