`u = -21i` Use the dot product to find the magnitude of u.
The magnitude of a vector `u` is the square root of its dot product by itself, because
`u*u=||u||*||u||*cos(theta),` and `theta=0,` `cos(theta)=1.`
I suppose that the magnitude of `i` is 1. Then
This is the answer.
There's no way to have a dot product, because there is only one vector. A dot product is two vectors multiplied together.
Using the Pythagorean theorem...
where a is the x coordinate, b is the y coordinate, and c is the length of the vector.
after taking the square root of both sides.
`21 ` is the magnitude