I need to provide both geometric and algebraic arguments that these vectors are linearly dependent.

a = 1 b = o c = -3

-1 2 5

Now if this could be put into a square matrix I would know just how to get the determinant and show that it is = 0 and I would have the algebraic part done. I can not figure out how do check the determinant of a nonsquare matrix. Any advice? THanks Frostking