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: 41

Answer

Dependent; $x=2-3t$ $y=3-5t$ $z=t$

Work Step by Step

$ \begin{bmatrix} 2 & -3 & -9 & -5\\ 1 & 0 & 3 & 2\\ -3 & 1 & -4 & -3 \end{bmatrix} $ Interchange the 1st and the 2nd row. $ \begin{bmatrix} 1 & 0 & 3 & 2\\ 2 & -3 & -9 & -5\\ -3 & 1 & -4 & -3 \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 & 0 & 3 & 2\\ 0 & -3 & -15 & -9\\ 0 & 1 & 5 & 3 \end{bmatrix} $ Interchange the 2nd row and the 3rd row. $ \begin{bmatrix} 1 & 0 & 3 & 2\\ 0 & 1 & 5 & 3\\ 0 & -3 & -15 & -9 \end{bmatrix} $ Add 3 times the 2nd row to the 3rd row. $ \begin{bmatrix} 1 & 0 & 3 & 2\\ 0 & 1 & 5 & 3\\ 0 & 0 & 0 & 0 \end{bmatrix} $ $\rightarrow$ Dependent system From the last row we got the equation $0=0$ which is always true and therefore the system has infinitely many solutions but x,y and z cannot be any random numbers. To describe the complete solution of the system of equations, let $z=t$ where t is any real number. Use back-substitution to find the solution. $z=t$ $y+5z=3\rightarrow y=3-5t$ $x+3y=2 \rightarrow x=2-3t$
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