99.9×99.9怎么巧算?
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99.9×99.9怎么巧算?
99.9×99.9怎么巧算?
99.9×99.9怎么巧算?
99.9×99.9=(100-0.1)^2=100^2-0.1^2=10000-0.01=9999.99
(100-0.1)^2
99.9×99.9
=(100-0.1)×(100-0.1)
=100×100-2×100×0.1+0.1×01.
=10000-20+0.01
=9980+0.01
=9980.01