199.9x199.9-200x199.8
=199.9x199.9-200x(199.9-0.1)
=199.9x199.9-200x199.9+200x0.1
=199.9x(199.9-200)+20
=199.9x(-0.1)+20
=-19.99+20
=0.01
199.9*199.9 - 200*199.8
= (200*199.9-0.1*199.9) - (200*199.9-200*0.1)
=-0.1*199.9 -(-200*0.1)
=(200-199.9)*0.1=0.1*0.1=0.01;
典型的数学行为
199.9×199.9-200×199.8
=199.9×199.9-(199.9+0.1)×199.8
=199.9×199.9-199.9×199.8-0.1×199.8
=199.9×(199.9-199.8)-19.98
=199.9×0.1-19.98
=19.99-19.98
=0.01
如果知道平方差公式:(a+b)(a-b)=a²-b²
那么
原式
=199.9²-(199.9+0.1)×(199.9-0.1)
=199.9²-(199.9²-0.1²)
=0.1²
=0.01
=0.01 199.9×199.9=39960.01 200×199.8=39960
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