Given a and b are unit vectors, if the angle between them is 60, determine $\displaystyle (6a + b) \cdot (a - 2b)$
I have no idea how to do it. Plugging it in to the standard formula where 60 is the angle does not give the correct answer.
Given a and b are unit vectors, if the angle between them is 60, determine $\displaystyle (6a + b) \cdot (a - 2b)$
I have no idea how to do it. Plugging it in to the standard formula where 60 is the angle does not give the correct answer.
Well,
expand by respective dot product (6a+b)(a-2b)
Pretty much like the normal numbers expansion ( Keep it ordered though )
Then a(dot)a=1
b(dot)b=1
a(dot)b=lengtha * lengthb * cos60
but a, b unit vectors with 1 unit lengths each
Proceed ...
Good Luck.
PS: Wherever you come to let us say
6a(dot)b =6(a(dot)b) can take the constant coeff. out,
a(dot)b=[b (dot) a]=you know what !