System of equations

Question

The following system is solved by substitution. Which expression is substituted for z in the second and third equations?

x + 4y + z = -10
3x - 3y + 6z = -21
x + 2y + 2z = -10

Answer 1

First, make sure you have copied down the equations correctly.

Solve the first equation, by keeping 'z' on the left side of the equal sign while you subtract 'x' and '4y'.

z = - x - 4y - 10

You can now substitute for 'z' in the 2nd and 3rd equations.

2nd equation:  3x - 3y + 6 (- x - 4y - 10) = - 21

3rd equation:  x + 2y + 2(- x - 4y - 10) = - 10

 

You simply asked for how to get started.  That sounds like you are willing to finish it, once you know how to start the problem.  Perseverance is a good approach.  Good luck.                

Mary Ann