Question

Find the vector , knowing that its modulus is 5, and it is orthogonal to x axis. and .=6 and =i+2j

Answer 1

being orthogonal to the x axis means it is parallel to the y axis so it is a scalar multiple of the unit vector in that direction, <j>.
so it is of the form k<j> and can be written 0i+kj
so dotting it with <w>, you get 0(1) + 2(k) = 6 according to what the problem says
Therefore, 2k=6
so k=3
so the vector <v>=3j

Answer 2

Does that help?

Answer 3

yes this helped me a lot. thanks.