Question

对于有理数a,b,a*b=3a+2b,则[(x+y)*(x-y)]*3x化简后得 A 0 B 5x C 21x+3y D 9x+6y 请大家帮我解决，讲解一

Answer 1

答：
选C
由a*b=3a+2b,得：(x+y)*(x-y)=3(x+y)+2(x-y)=5x+y
[(x+y)*(x-y)]*3x=(5x+y)*3x
=3(5x+y)+2(3x)
=15x+3y+6x
=21x+3y
C符合。