00:01
Okay, let's solve this system.
00:02
Now, i would start with the middle equation because of that single variable of z.
00:09
It tells me i could easily solve that equation for z.
00:13
So all i have to do is subtract 4y from both sides, and i get z equals negative 4y plus 7.
00:24
So i'm going to substitute this in for the only equation here, other equation that has a z.
00:32
And that's the third one.
00:34
So i'll try to use some colors to show that substitution.
00:38
So negative 8x plus, here it comes, instead of z, we're going to write negative 4y plus 7, and that equals negative 4.
00:51
So let's clean it up.
00:53
We could subtract 7 from both sides, and i get negative 8x minus 4y equals negative 11.
01:04
So the first equation also has an x and a y as its variables.
01:09
So we're going to use those two equations together.
01:12
So i'll write that first equation underneath this new one.
01:19
And what i want to do is multiply one of the equations by a constant so that when i add them, that term will cancel out.
01:28
So i could multiply this bottom equation by 2.
01:32
That would give me 8x minus 16y equals negative 4.
01:38
And the top equation would remain the same.
01:47
I'm going to add those two equations.
01:49
The x's would make a 0 and i get negative 20y equals negative 25...