00:01
Alright, this is going to be problem number 17.
00:04
X minus y minus z equals 4.
00:10
2 y plus z equals negative 1.
00:16
And negative x plus y minus 2 z equals 5.
00:22
So your goal here is to decide what you want to eliminate.
00:28
So i looked at the first equation, x minus y minus z equals 4.
00:35
And the last equation, negative x plus y minus 2 z equals 5.
00:41
Because when i see the x minus x and the negative y plus y they become zero.
00:48
They cancel each other out.
00:50
So then i am left with negative z minus 2 z.
00:53
So that is a negative 3 z.
00:55
And 4 plus 5 equals 9.
00:58
So you just do what it says.
00:59
You don't change anything there.
01:02
Divide by negative 3.
01:06
So z is negative 3.
01:10
Then since you know z is negative 3 you might as well take that and substitute it back into the second equation.
01:19
And now you can solve for y.
01:21
So i am going to add 3 to each side.
01:23
3 minus 1 is 2.
01:25
If 2 y equals 2 i will divide each side by 2 and y is 1.
01:30
And now that i know what y and z are i can plug them back into the original first equation and solve for x.
01:42
Let's say it would be a positive 3 minus 1 which is 2.
01:46
Subtracting 2 from each side x is going to be negative, excuse me, x is going to be positive 2...