199.5乘199.4减199.1乘199.8
=(199.8-0.3)x199.4-199.8x199.1
=199.8x199.4-0.3x199.4-199.8x199.1
=199.8x(199.4-199.1)-199.4x0.3
=199.8x0.3-199.4x0.3
=(199.8-199.4)x0.3
=0.4x0.3
=0.12
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[(200-0.5)x(200-0.6)]-[(200-0.9)x(200-0.2)]
=[(200x200)-(0.5x0.6)]-[(200x200)-(0.9x0.2)]
=(40000-3)-(40000-1.8)
=1.2