`u = 20i + 25j` 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 `i` and `j` are orthonormal. Therefore

`||u||=sqrt(u*u)=sqrt((20i+25j)*(20i+25j))=`

`=sqrt(20*20+25*25)=5sqrt(4*4+5*5)=5sqrt(41) approx 32.`

This is the answer.

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 `i` and `j` are orthonormal. Therefore

`||u||=sqrt(u*u)=sqrt((20i+25j)*(20i+25j))=`

`=sqrt(20*20+25*25)=5sqrt(4*4+5*5)=5sqrt(41) approx 32.`

This is the answer.