Question

Which of the following vectors are orthogonal to (1,5)? Check all that apply
a. (-2,5)
b. (-5,1)
c.(-1,-5)
d. 10,-2)
I'm thinking b and d, can someone confirm whether or not any of the others work and whether or not I'm right?

Answer 1

do you know how to do a dot product?
the dot product of 2 vectors that are orthogonal will be zero.

Answer 2

for example, <-2,5> dot <1,5>= -2*1 +5*5= -2+25= 23
that is not zero, so not choice A

Answer 3

Pretty sure it would be "B and D"

Answer 4

Ah, I think I got it!
(-5,1) and (1,5) =-5+5=0
(-1,-5) and (1,5)=-1+-25=-26
(10,-2) and (1,5)=10+-10=0

Answer 5

Yeah you got it :) Just make sure you show them as vectors and not points!

Answer 6

Good job!