Consider the following system of three equations in three unknowns.
2x − y + z = −9
x + y + 4z = −17
3x + 4y − z = 2
(a) Solve the first equation for z.
z = -9-2x+y
(b) Put the solution you got in part (a) for z into both the second and third equations. Solve each equation for y.
2nd equation y = (19+7x)/5
3rd equation y = (-7-5x)/3
(c) Solve the system of two equations in two unknowns that you found in part (b).
(d) Write the solution of the original system of three equations in three unknowns.
I'm not quite sure how to get the points. Do I use the second or first equation, substitute y and z and solve for x? I don't even know how to begin to solve for z...