Given vectors u= -7i + 4j and v= 8i + 9j, find 5u - 9v in terms of unit vectors i and j.

Question

xapproachesinfinity · Answer

any thoughts

anonymous · Answer

i got -60i - 108j

xapproachesinfinity · Answer

what did you do

xapproachesinfinity · Answer

i can't say you are right or wrong unless i do it

anonymous · Answer

I got both the numbers but in my choices i didn't know which one to choose since I honestly just winged it. :( 

my choices are 
-104i - 108j 
-107i -61j 
-66i -108j
- 60 - 108j

xapproachesinfinity · Answer

seems you got the last choice

xapproachesinfinity · Answer

D

freckles · Answer

do you know how to find 5u?

freckles · Answer

c= or the other notation (in terms of the unit vectors) c(ai+bj)=(ca)i+(cb)j

anonymous · Answer

I first did 5(-7 + 4j) - 9(8i +9j) but I realized none of my answers were in the choices so I switched 9 and 5.

amity · Answer

Correct answer is-107i-61j..

5(-7i+4j)-9(8i+9j)=(-35-72)i +j(-81+20)=-107i-61j

amity · Answer

Correct answer is-107i-61j..

5(-7i+4j)-9(8i+9j)=(-35-72)i +j(-81+20)=-107i-61j

xapproachesinfinity · Answer

what you did in the beginning is correct

xapproachesinfinity · Answer

5u=5(-7i+4j)=-35i+20j

xapproachesinfinity · Answer

-9v=-9(8i+9j)=-72i-81j

anonymous · Answer

yes i got that

xapproachesinfinity · Answer

combine them
5u-9v=-35i+20j-72i-81j=-107i-61j

xapproachesinfinity · Answer

apparently that's the second choice

anonymous · Answer

ooh i forgot i had to combine them. i was seriously just adding 35 and 20. thank you!

xapproachesinfinity · Answer

no problem