x+3分之2+3-x分之2+x^2-9分之2x+18
2 2 2x+18
= --- - --- + --------
x+3 x-3 x²-9
2x-3-2x-6+2x+18
= －－－－－－－－－－
x²-9
2x+6
= ----------
(x-3)(x+3)
= 2/x-3
由于是整数,所以x-3=1 2 -1 -2
x=4 5 2 1 he是=12
2,3题自己做!别偷懒!
4 a=4.012=4 3/250
a^2+b^2+c^2-ab-bc-ca=1/2[（a-b）²+（b-c）²+（c-a）²]
=1/2（2²+1²+1²）=3