Tuesday, June 30, 2015

Simultaneous equation practice with Kramer's rule


6x + 5y = 18
2x - y = -4

3x + 7y = 12
2x + 5y = -18

Answers in the comments.

1 comment:

Prof. Hubbard said...

6x + 5y = 18
2x - y = -4

First determinant (denominator)

| 6 5|
| 2 -1| = -6 -10 = -16

Swap out x column

| 18 5|
| -4 -1| = -18 +20 = 2


Swap out y column

| 6 18|
| 2 -4| = -24 - 36 = -60

So x = 2/-16 = -1/8
and y = -60/-16 = 15/4 = 3 3/4


=========

3x + 7y = 12
2x + 5y = -18

First determinant (denominator)

| 3 7|
| 2 5| = 15 - 14 = 1

Swap out x column

| 12 7|
| -18 5| = 60 + 126 = 186


Swap out y column

| 3 12|
| 2 -18| = -54 - 24 = -78

So x = 186/1 = 186
and y = -78/1 = -78