Answer:B
Step-by-step explanation:
....................First 3
And i didnt copy u kishaabbas
One could use the relation

where

are two vectors,

denotes the norm of that vector, and

is the angle between the two vectors.
Then the two vectors will be parallel if

or

.
Answer:
theres nothing? :/
Step-by-step explanation:
Ok so if you notice every choice is solved for a, all you have to do is isolate "a" in 7a-8b=10x. Start by moving 8b to the other side and to change the sign. Now it is 7a = 10x + 8b. Then divide everything by 7 and you get a = (10x + 8b)/7