Question

determine vectors u and v are parallel ,orthogonal or neither
u=(2,5) v=(10/3,4/3)
please use ab=|a|•|b|•cos theta to solve this problem!!! thx

Answer 1

c'mon. They are orthogonal if u•v = 0
And we know you can do dot products.
parallel if u•v = |u| * |v|

Come back with your work if you get stick.

Answer 2

but we don't know cos theta. How to calculate dot product?

Answer 3

Ummmmhhhh,
eg.
(a,b)•(c,d) = ac + bd

you have the numbers.

btw, your question says:
ab=|a|•|b|•cos
bad notation used here
it should be

a•b = |a||b|cos theta

Answer 4

i and j are x and y directions
if u = ux i + uy j
and v = vx i + vy j
then
u dot v = ux vx + uy vy

Answer 5

like the second way here
https://www.mathsisfun.com/algebra/vectors-dot-product.html