Precalculus: Mathematics for Calculus, 7th Edition

Published by Brooks Cole
ISBN 10: 1305071751
ISBN 13: 978-1-30507-175-9

Chapter 10 - Section 10.3 - Matrices and Systems of Linear Equations - 10.3 Exercises - Page 710: 36

Answer

$x=3$ $y=1$ $z=1$

Work Step by Step

$ \begin{bmatrix} 2 & 1 & 0 & 7\\ 2 & -1 & 1 & 6\\ 3 & -2 &4 & 11 \end{bmatrix} $ Divide the 1st row by 2. $ \begin{bmatrix} 1 & \frac{1}{2} & 0 & \frac{7}{2}\\ 2 & -1 & 1 & 6\\ 3 & -2 &4 & 11 \end{bmatrix} $ Add -2 times the 1st row to the 2nd row to produce a new 2nd row. Add -3 times the 1st row to the 3rd row to produce a new 3rd row. $ \begin{bmatrix} 1 & \frac{1}{2} & 0 & \frac{7}{2}\\ 0 & -2 & 1 & -1\\ 0 & -\frac{7}{2} &4 & \frac{1}{2} \end{bmatrix} $ Divide the second row by -2. $ \begin{bmatrix} 1 & \frac{1}{2} & 0 & \frac{7}{2}\\ 0 & 1 & -\frac{1}{2} & \frac{1}{2}\\ 0 & -\frac{7}{2} &4 & \frac{1}{2} \end{bmatrix} $ Add $\frac{7}{2}$ times the 2nd row to the 3rd row. $ \begin{bmatrix} 1 & \frac{1}{2} & 0 & \frac{7}{2}\\ 0 & 1 & -\frac{1}{2} & \frac{1}{2}\\ 0 & 0 &\frac{9}{4} & \frac{9}{4} \end{bmatrix} $ Use back-substitution to find the solution. $\frac{9}{4}z=\frac{9}{4} \rightarrow z=1$ $-2y+z=-1\rightarrow y=1$ $2x+y=7 \rightarrow x=3$
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