Intermediate Algebra for College Students (7th Edition)

Published by Pearson
ISBN 10: 0-13417-894-7
ISBN 13: 978-0-13417-894-3

Chapter 3 - Section 3.3 - Systems of Linear Equations in Three Variables - Exercise Set - Page 216: 28

Answer

The numbers are $-1,2$ and $3$.

Work Step by Step

Let the three numbers be $a,b$ and $c$. From the question we have $\Rightarrow 3a+b+2c=5$ ...... (1) $\Rightarrow (a+3c)-3b=2$ Rearrange. $\Rightarrow a-3b+3c=2$...... (2) $\Rightarrow (2a+3b)-c=1$ Rearrange. $\Rightarrow 2a+3b-c=1$ ...... (3) Multiply equation (3) by $2$. $\Rightarrow 2(2a+3b-c)=2(1)$ $\Rightarrow 4a+6b-2c=2$...... (4) Add equation (1) and (4). $\Rightarrow 3a+b+2c+4a+6b-2c=5+2$ $\Rightarrow 7a+7b=7$ Divide the equation by $7$. $\Rightarrow a+b=1$...... (5) Multiply equation (5) by $-6$ $\Rightarrow -6a-6b=-6$...... (6). Multiply equation (3) by $2$. $\Rightarrow 3(2a+3b-c)=3(1)$ $\Rightarrow 6a+9b-3c=3$...... (7) Add equation (2) and (6). $\Rightarrow a-3b+3c+6a+9b-3c=2+3$ $\Rightarrow 7a+6b=5$...... (8). Add equation (6) and (8). $\Rightarrow -6a-6b+7a+6b=-6+5$ Simplify. $\Rightarrow a=-1$ Substitute the value of $a$ into equation (5). $\Rightarrow -1+b=1$ Add $1$ to both sides. $\Rightarrow -1+b+1=1+1$ Simplify. $\Rightarrow b=2$ Substitute the values of $a$ and $b$ into equation (1). $\Rightarrow 3(-1)+2+2c=5$ Simplify. $\Rightarrow -3+2+2c=5$ $\Rightarrow -1+2c=5$ Add $1$ to both sides. $\Rightarrow -1+2c+1=5+1$ Simplify. $\Rightarrow 2c=6$ Divide both sides by $2$ $\Rightarrow c=3$
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