Angles between unit vectors

[RM5152]

Hello. I think I have solved the first part of this question but can’t figure out how to find the points for y to be able to answer question (b): multiply y.(7x+3y) or how to find question (c): the Length of 2x-9y. Can someone please help? Thank you ?

 

[Deleted member 4993]

Hello. I think I have solved the first part of this question but can’t figure out how to find the points for y to be able to answer question (b): multiply y.(7x+3y) or how to find question (c): the Length of 2x-9y. Can someone please help? Thank you ?View attachment 33174View attachment 33175

Hint:

y \(\displaystyle \cdot\)y = 1................... and.................... y \(\displaystyle \cdot\)x = x \(\displaystyle \cdot\)y

 

[Steven G]

You need to try something!
y*(7x+3y) = y*7x + y*3y = 7(y*x) + 3(y*y)
You are given what x*y equals and should know what y*y equals.