PP-T1-DS146

[Huang Hsin-Yi]

146. 14746-!-item-!-187;#058&010097
If the symbol @ represents either addition or multiplication, which operation does it represent?

(1) a@b=b@a for all numbers a and b.

(2) a@(b-c)=(a@b)-(a@c) for all numbers a, b, and c.

Ans:B

請問題目再問什?

[sunnyblue13s]

他問你@...到底是"+" 還是"*"

[Huang Hsin-Yi]

感恩
(1)a+b=b+a
a*b=b*a
therefore @=+,*.................................insufficient
(2)a+(b-c)=/=(a+b)-(a+c)
a*(b-c)=a*b-a*c
therefore @=*.......................................sufficient