00:01
So let's start with the first two equations.
00:03
We've got x plus 3y minus 6 z equals 7.
00:19
And we've got 2x minus y plus z equals 1.
00:36
So what i'd like to do with these is to eliminate the x terms.
00:40
Now i want to do that is i'm going to multiply the top equation by a negative 2.
00:46
Then add them together.
00:47
So i do that.
00:48
I have zero here for my x term.
00:50
I'm just not going to write that down.
00:51
I'm just going to talk about that one.
00:54
And then we have a negative 6 minus y, so negative 7y.
01:02
Negative 2 times negative 6 is positive 12 plus 1 is positive 13 z.
01:13
And i have a negative 14 plus 1 is going to equal negative 13.
01:20
So now i'm actually going to take this first equation again, x, 3y, minus 6 z, equal 7.
01:41
And then i'm going to take the last equation, which is x plus 2y plus 2z equals negative 1.
02:05
So again, i'm trying to eliminate that x term, and i think i'm going to do it by multiplying the top by a negative 1 this time.
02:12
So again, it all cancel my x's...