Question

对于有理数a，b，定义a*b=3a+2b,则(x+y)*(x-y)*3x化简后得什么 A.0 B.5X C.21X+3y D.9x+6y

要过程，详细点

Answer 1

a*b=3a+2b
(x+y)*(x-y)=3(x+y)+2(x-y)=3x+3y+2x-2y=5x+y
(x+y)*(x-y)*3x=(5x+y)*3x
=3(5x+y)+6x
=15x+3y+6x
=21x+3y
答案： C.21X+3y

Answer 2

(x+y)*(x-y)=3(x+y)+2(x-y)=5x+y
(5x+y)*3x=3(5x+y)+2*3x=15x+3y+6x=21x+3y
所以选C

Answer 3

(x+y)*(x-y)=3(x+y)+2(x-y)=5x+y
(5x+y)*3x=3(5x+y)+6x=21x+3y
所以选C

Answer 4

解析：
(x+y)*(x-y)*3x=[3(x+y)+2(x-y)]*3x=(5x+y)*3x=3(5x+y)+2(3x)=21x+3y。
所以，答案选C。