(1)999²-1001²(2)(99 1/2)²-(100 1/2)².
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(1)999²-1001²(2)(99 1/2)²-(100 1/2)².
(1)999²-1001²
(2)(99 1/2)²-(100 1/2)².
(1)999²-1001²(2)(99 1/2)²-(100 1/2)².
用公式a^2-b^2=(a+b)(a-b)
(1)999²-1001²=(999-1001)(999+1001)=2000(-2)=-4000
(2)(99 1/2)²-(100 1/2)²=(99 1/2-100 1/2)(99 1/2+100 1/2)=200(-1)=-200