Question

replace the third equation by the sum of itself and -1 times the second equation x-2y-7z=17,-6x+4y+5z=-9,8x+7y=z=-4

Answer 1

`14x+3y-6z=5`

Explanation:

`x-2y-7z=17` --- 1

`-6x+4y+5z=-9` --- 2

`8x+7y-z=-4` ---3

-1 times the second equation =
`-1(-6x+4y+5z=-9)`

=
`6x-4y-5z=9` --4

Now we are given that replace the third equation by the sum of itself and -1 times the second equation

So, New third equation =
`8x+7y-z+6x-4y-5z=-4+9`

=
`14x+3y-6z=5`

Hence the new third equation is
`14x+3y-6z=5`