求NN解释？？~~

mingminglous

For all integers x and y, the operation D is defined by xDy = (x+2)2 + (y+3)2.What is the value of integer t?
(1)t D 2 = 74
(2)2 D t = 80

A. Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient.
B. Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient.
C. BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient.
D. EACH statement ALONE is sufficient.
E. Statements (1) and (2) TOGETHER are NOT sufficient.

小弟觉得应该是D吧，两个独立都可以得到答案，为什么答案说是C呢，求NN解释

mingminglous

谢谢，做题时忽略了这个问题~~

zhouyeying

开平方你要考虑正负啊 ， 题目只说integer 没说是positive integer 啊

Vickyliu

确定一个t值，t只能是一个数，不能是 或