=(10000-9999-3)2 =(-2)2 =4
28 m2-mn+n2 =(m+n)2-3mn =64-45 =19
29. 1) ∵a2+a-1=0 ∴a2+a=1 ∴2a2+2a =2(a2+a) =2×1 =2 2) a2+a-1=0
则 a*(a2+a-1)=a3+a2-a=0---------A a2+a-1=0 -----------B A+B得 a3+2a2-1=0 a3+2a2=1
所以 a3+2a2+1999=1+1999=2000 30
x2-x-x2+y=-2 -x+y=-2 x-y=2
(x2+y2)/2-xy =(x2-2xy+y2)/2 =(x-y)2/2 =(2)2/2 =4/2 =2
5
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