Answer:
2
Step-by-step explanation:
come on man if you are in -2 dollar debt and someone gives you 4 more dollars you now have 2 dollars
Answer:
A. {u1,u2,u3,u4} is a linearly independent set of vectors unless one of {u1,u2,u3} is the zero vector.
Step-by-step explanation:
Given that u4 is not a linear combination of {u1,u2,u3}
This means there is no possibility to write u4 = au1+bu2+cu3 for three scalars a,b,and c.
This gives that 
This implies that these four vectors are not linearly dependent but linearly independent.
Hence option a is right.
A. {u1,u2,u3,u4} is a linearly independent set of vectors unless one of {u1,u2,u3} is the zero vector.
Sorry I don't have enough time to deal with this problems, I believe that by using this formula you will easily come out with your answer. In the first one that has all sides you must use the law of cosines. Here is the formulas . Keep it because it is very helpful