①1000²-998*1002(用简便方法计算)②(3x-4y)(-4y-3x)
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①1000²-998*1002(用简便方法计算)②(3x-4y)(-4y-3x)
①1000²-998*1002(用简便方法计算)
②(3x-4y)(-4y-3x)
①1000²-998*1002(用简便方法计算)②(3x-4y)(-4y-3x)
①1000²-998*1002(用简便方法计算)
=1000²-(1000-2)(1000+2)
=1000²-(1000²-4)
=4
②(3x-4y)(-4y-3x)
=-(3x-4y)(3x+4y)
=-(9x²-16y²)
=-9x²+16y²