计算题(1)(a+1/2b)²-(a-1/2b)² (2) (991/5)² (3) (x
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计算题(1)(a+1/2b)²-(a-1/2b)² (2) (991/5)² (3) (x+y)²-2(x+y)(x-y)+(x-y)²
(1)(a+1/2b)²-(a-1/2b)²
= (a+b/2+a-b/2)(a+b/2-a+b/2)
=2ab
(2) (991/5)²
=(1000-9)^2/25
=(10^6-18000+81)*4/100
=40000-720+3.24
=39283.24 .
(3) (x+y)²-2(x+y)(x-y)+(x-y)²
=[x+y-x+y]^2
=4y^2
= (a+b/2+a-b/2)(a+b/2-a+b/2)
=2ab
(2) (991/5)²
=(1000-9)^2/25
=(10^6-18000+81)*4/100
=40000-720+3.24
=39283.24 .
(3) (x+y)²-2(x+y)(x-y)+(x-y)²
=[x+y-x+y]^2
=4y^2
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