Thinking Mathematically (6th Edition)

Published by Pearson
ISBN 10: 0321867327
ISBN 13: 978-0-32186-732-2

Chapter 5 - Number Theory and the Real Number System - 5.5 Real Numbers and Their Properties; Clock Addition - Exercise Set 5.5 - Page 309: 57

Answer

Properties used are distributive, commutative, associative, distributive and commutative, respectively.

Work Step by Step

Consider the expression and evaluate it as, \[5\left( x+4 \right)+3x=\left( 5x+20 \right)+3x\ \ \ (why?)\] \[5\]is distributed over\[x\]and\[4\]. Thus, distributive property is used. \[\begin{align} & 5\left( x+4 \right)+3x=\left( 5x+20 \right)+3x\ \ \ (\text{distributive property}) \\ & =\left( 20+5x \right)+3x\ \ \ (why?) \end{align}\] Order of addition is changed in \[\left( 5x+20 \right)\]. Thus, commutative property of addition is used. \[\begin{align} & 5\left( x+4 \right)+3x=\left( 5x+20 \right)+3x\ \ \ (\text{distributive property}) \\ & =\left( 20+5x \right)+3x\ \ \ (commutative\ property) \\ & =20+\left( 5x+3x \right)\ \ \ (why?) \end{align}\] Associative property of addition is used as \[\left( 5x+3x \right)\] and is added first. \[\begin{align} & 20+\left( 5x+3x \right)=20+x\left( 5+3 \right)\ \ \ (why?) \\ & =20+8x \end{align}\] \[\left( 5+3 \right)\]is distributed over \[x\]. Thus, distributive property is used. \[20+8x=8x+20\ \ \ (why?)\] Order of addition is changed in \[\left( 20+8x \right)\]. Thus, the commutative property of addition is used. Hence, properties used are distributive, commutative, associative, distributive and commutative respectively.
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