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(2,3,-2)

Step-by-step explanation:

3x+y+z = 7

x+3y-z =13

y = 2x-1

Add the first two equations together to eliminate z

3x+y+z = 7

x+3y-z =13

4x+4y = 20

Divide by 4

4x/4 + 4y/4 = 20/4

x+y = 5

We know y = 2x-1.  substitute this into the equation

x+ (2x-1) = 5

Combine like terms

3x-1 =5

Add 1 to each side

3x-1+1 =5+1

3x=6

Divide by 3

3x/3 = 6/3

x=2

Now we can find y

y = 2x-1

y = 2(2)-1

y =4-1

y= 3

We know x and y, now we need to find z

3x+y+z = 7

3(2) +3 +z = 7

6+3+z =7

9+z=7

Subtract 9 from each side

-9+z =7-9

z=-2

So x=2,y=3 =-2

(2,3,-2)

y - 1 = -3(x - 2)

Step-by-step explanation:

Sounds as though you want the equation of the line through (2, 1) and (5, -8).

As we move from (2, 1) to (5, -8), x (the "run") increases by 3 and y (the "rise") decreases by 9.  Thus, the slope of this line is m = rise / run = -9/3, or m = -3.

Let's use the point-slope formula for a straight line here:  The point (h, k) is (2, 1) and the slope is -3. Then y - k = m(x - h) becomes:

y - 1 = -3(x - 2)