WEBVTT

1
00:00:00.000 --> 00:00:10.078
Here is the problem: 7x minus 7y equals negative 14 over 3; negative 2x plus 8y equals negative 14 over 3.

2
00:00:10.527 --> 00:00:13.627
2 linear equations in 2 unknowns (x, y).

3
00:00:14.427 --> 00:00:20.638
Write every equation in standard form. Move all variable terms to the left and constants to the right.

4
00:00:21.088 --> 00:00:25.395
Build the augmented matrix [A | b]. Columns: x, y | constant.

5
00:00:25.845 --> 00:00:32.288
Gauss–Jordan elimination. Use row operations to make each pivot 1 and clear the rest of its column.

6
00:00:32.739 --> 00:00:34.713
Divide R1 by 7.

7
00:00:35.513 --> 00:00:38.346
Clear column 1 using the pivot in R1.

8
00:00:38.796 --> 00:00:40.642
Divide R2 by 6.

9
00:00:41.092 --> 00:00:43.925
Clear column 2 using the pivot in R2.

10
00:00:44.375 --> 00:00:46.221
Reduced row-echelon form.

11
00:00:47.021 --> 00:00:48.646
Read off the unique solution.

12
00:00:49.446 --> 00:00:54.612
So the answer is x equals negative 5 over 3, y equals negative 1.

13
00:00:55.062 --> 00:01:00.681
The system has exactly one solution; substituting it back satisfies every equation.

14
00:01:01.481 --> 00:01:07.785
Equation 1: 7x minus 7y equals negative 14 over 3, which checks out.

15
00:01:08.235 --> 00:01:14.969
Equation 2: negative 2x plus 8y equals negative 14 over 3, which checks out.
