Step by step
The question
Question: find the unit vector in the direction of v = ⟨−3, −4⟩.
1 Draw the arrow
Draw the grid.
The arrow starts at the origin.
It goes left 3 and down 4.
Across 3 and down 4 make a right triangle.
2 Find the length
The length ‖v‖: the long side of the right triangle.
Pythagoras: square the two parts, add them, then take the square root.
Write the squares: 9 + 16.
9 plus 16 is 25.
5 times 5 is 25.
So ‖v‖ = 5.
3 Divide by the length
To make the length 1, divide each part by the length, 5.
The direction stays the same.
Careful!
Not 1 in each part.
The length must be 1, and the arrow must point the same way as v.
So u = ⟨−3/5, −4/5⟩.
On the grid, u is a short arrow along v: length 1.
4 Check
Let's check: the length of u must be 1.
Square the parts and add them.
We get 1.
So the length of u is 1.
Right!
Let's look back.
First: draw the arrow.
Then: find the length.
Then: divide by the length.
Last: check.