Question

Solve the system. -3x-y=10; y-4z=-13; x-4y+z=4

Answer 1

9514 1404 393

Answer:

  (x, y, z) = (-3, -1, 3)

Step-by-step explanation:

Many graphing calculators can solve matrix equations handily. Here, we use a combination of methods.

Use the last equation to write an expression for z.

  z = 4 -x +4y

Substitute this into the second equation:

  y -4(4 -x +4y) = -13

  y -16 +4x -16y = -13

  4x -15y -3 = 0

In genera form, the first equation can be written as ...

  3x +y +10 = 0

Now, the solution to these two equations can be found to be ...

  x = (-15(10) -1(-3))/(4(1) -3(-15)) = (-150 +3)/(4+45) = -3 . . . using "Cramer's rule"

  y = -(10 +3x) = -(10 -9) = -1 . . . . from the first equation

  z = 4 -(-3) +4(-1) = 3 . . . . . . . . from our equation for z

The solution to the system is (x, y, z) = (-3, -1, 3).

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Additional comment

Written as an augmented matrix, the system of equations is ...

  $\left[\begin{array}{ccc|c}-3&-1&0&10\\0&1&-4&-13\\1&-4&1&4\end{array}\right]$