SAT数学题求讲解For all real numbers v,the operation v * is defined by the equation v*= v-3.If (v*)*=8,then v =A 15 B 18 C 21 D 24 E 27

2019-05-23

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SAT数学题求讲解
For all real numbers v,the operation v * is defined by the equation v*= v-3.If (v*)*=8,then v =
A 15 B 18 C 21 D 24 E 27

优质解答

题目有错
原题应为“…… by the equation v*= v-v/3.If (v*)*=8……”
∵v*= v-v/3
∴v*= 2/3 v
∵ (v*)*=8
∴(v*)*=2/3 v*=2/3 (2/3 v)=4/9 v=8
∴v=18 题目有错
原题应为“…… by the equation v*= v-v/3.If (v*)*=8……”
∵v*= v-v/3
∴v*= 2/3 v
∵ (v*)*=8
∴(v*)*=2/3 v*=2/3 (2/3 v)=4/9 v=8
∴v=18