Vector Question:

Let v=(2,8) and w=(-1,-4). Which of the following is true? Check all that apply.

http://gyazo.com/e70e77c91c6c709f192906a77ae6f811

Answer choices above ^

Question

Vector Question:

Let v=(2,8) and w=(-1,-4). Which of the following is true? Check all that apply.

http://gyazo.com/e70e77c91c6c709f192906a77ae6f811

Answer choices above ^

dumbcow · Answer

ok are there any you already know are true?

dumbcow · Answer

hint:
vectors are only perpendicular when dot product equals 0

dumbcow · Answer

http://en.wikipedia.org/wiki/Dot_product#Algebraic_definition

anonymous · Answer

I know that A and B are true, correct?

anonymous · Answer

@dumbcow

dumbcow · Answer

yes A and B are true

using my hint, what can you say then about option C

anonymous · Answer

C would not be true, because the Dot Product is -34.

dumbcow · Answer

correct
now look at D ... multiply vector w by -2 ... what do you get?

anonymous · Answer

w=(2,8)

dumbcow · Answer

right which is equal to v, so D is true as well

anonymous · Answer

Alright, thank you for your help! ^_^