Answer:
Let's define:
s1 = (3, 4)
s2 = (-1, 1)
s3 = (2, 0)
The system will be linearly dependent if we can write one of the vectors as a linear combination of the other two, so for example:
s1 = a*s2 + b*s3
where a and b are real numbers.
So let's try to solve this:
(3, 4) = a*(-1, 1) + b*(2, 0)
Note that the second term in the left only modifies the x-component. And the y-component in the left is 4, so we can conclude that a = 4 (because the first term is the only that has an y-component different than zero)
(3, 4) = 4*(-1, 1) + b*(2, 0)
(3, 4) = (-4, 4) + b*(2, 0)
Now we need to solve:
3 = -4 + b*2
3 + 4 = b*2
7 = b*2
7/2 = b
Then the linear combination is:
s1 = 4*s2 + (7/2)*s3
(3, 4) = 4*(-1, 1) + (7/2)*(2, 0)
Then the set is linearly dependent.
