00:01
So in this problem, we're given three equations, three unknowns in this system of linear equations, and asked to solve them algebraically.
00:11
So first i'm going to draw a line here just to keep our work kind of neat.
00:16
And i want to designate this first one is equation one, the next one equation two, and the next one equation three.
00:23
So now we need to combine these so that we end up with two equations and two unknowns.
00:29
And so we can go after any of the variables we want, x, y, or z.
00:33
It looks like probably the xes might be the easiest.
00:37
And so let's take minus 3 times equation 1.
00:44
So that's minus 3x plus 6y minus 9z equals minus 12.
00:54
And then we'll add equation 2 to that.
00:57
So let's write equation 2 here.
00:59
3x minus y plus 2z equals 0.
01:06
Add these together.
01:08
Of course the x is drop out by design.
01:12
6y minus y, that's 5y.
01:15
Minus 9x plus 2z, that's minus 7z, and minus 12 plus 0 is still minus 12.
01:23
Okay.
01:26
I'm going to call this equation 4.
01:28
Now, let's take minus 3 times equation 3...