Question

Given vectors u=(3,5) and v=4,-4), determine the quantity -4u--2v

Answer 1

what is -4u?

Answer 2

i'm not sure... if it helps, the question looks like

Answer 3

-4u = -4(3,5) = (-4*3, -4*5) = (-12, -20)


So -4u = (-12, -20)


So what is -2v?

Answer 4

(-8,8)

Answer 5

good, so

-4u--2v

becomes

(-12, -20) - (-8,8)

Answer 6

then what's next?

Answer 7

do you subtract -12--8 and -20-8?

Answer 8

yes, you subtract the corresponding components

Answer 9

so then its (-4,-28)

Answer 10

bingo

Answer 11

but the answers that i have to choose from are round numbers like
-40
-256
-8
-64
88

Answer 12

hmm one sec while I reread it

Answer 13

maybe they want the dot product, I think i mistook that dot for a minus


So this means that

-4u dot -2v

becomes

(-12, -20) dot (-8,8)

which turns into

-12*(-8) + (-20)*(8) = 96 - 160 = -64

Answer 14

so -4u dot -2v = -64

Answer 15

oh, that makes more sense. i think that i did the same thing! no wonder it didn't work before.

Answer 16

yeah strange how they used a - (well a small - in my opinion) instead of a dot

Answer 17

yeah, i will have to keep an eye out for that next time. Thanks!

Answer 18

you're welcome