00:01
So we're given this system of equations here.
00:05
I'm going to take liberty of writing them down.
00:07
And we're asked to solve this algebraically.
00:11
All right, i'm going to call this equation one, equation two, and equation three.
00:17
And what do i notice? well, i notice that equation one does not have a y.
00:22
Two and three both have a y with the same coefficient.
00:26
So if i could subtract one from the other, then that would be gone.
00:32
And the result will just have x and z in it which i could use with equation one to solve so let's do equation two minus equation three so that's five x three y minus three y that's gone zero minus a negative four x four z that's four z and four minus four is zero i want to call this equation four so i want to combine equation 4 and equation 1 together.
01:08
And what do i notice? well, equation 1 has a 2z.
01:12
Equation 4 has a 4z.
01:14
So if i could do minus 2 times equation 1, i could add them together, and the zs would be gone, wouldn't they? all right, so minus 2 times 2x, that's minus 4x, minus 4z by design.
01:31
2 times minus 2, that's minus 4.
01:35
Add these together.
01:37
Of course the x's are gone, right? i'm sorry, not the x's.
01:41
Oops.
01:43
The zs will be gone.
01:44
The zs.
01:45
Z will be gone here...