two vectors are orthogonal (perpendicular), if their dot-product is zero
they're parallel, if they're just the product of scalar multiplication
like say hmmm <3, 7> and <12, 28> well 4*3 is 12, and 4*7 is 28
thus <12, 28> is really 4<3,7> so, those two are parallel
now.. let's check the dot-product on yours
<10, 0> • <0,-9> will be (10*0) + (0*-9) = 0 + 0 = 0 <--- orthogonal
