00:01
The topic of this question is systems of linear equations.
00:06
This question gives us a system of linear equations, which represents a system of electric currents within a circuit.
00:18
And so we want to find these three electric currents, i1, i2, and i3.
00:26
We can do this using either substitution or elimination of these three equations.
00:32
So since we have three equations with three unknowns, the first step is to find two equations with two unknowns.
00:39
So eliminate one of the variables into equations.
00:45
So an easy way to do that, an easy way to eliminate i2, for example, since it's already isolated here, is to substitute this equation into one of the others.
01:10
And so now we have one equation with just i1 and i3 as unknowns.
01:18
So now we need another equation with just i1 and i3.
01:23
And you may notice that we have negative 5 i2 here and a negative 5 i2 here.
01:30
And so we can use elimination, we can subtract these equations, or these bottom two equations, to eliminate i2 once again.
01:43
So let's do the bottom equation minus the top...