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问几道数学思考题⑴62又80/89×1/9⑵9又4/5+99又4/5+999又4/5+9999又4/5+4/5⑶2006

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问几道数学思考题
⑴62又80/89×1/9
⑵9又4/5+99又4/5+999又4/5+9999又4/5+4/5
⑶2006÷2006又2006/2007
⑷1×3+2×6+3×9+4×12+5×15/1×2+2×4+3×6+4×8+5×10
⑸84又4/19×1.375+105又5/19×0.9
⑹(1+1/2) ×(1-1/2) ×(1+1/3) ×(1-1/3) ×…×(1+1/100) ×(1-1/100)
⑺(1-1/2×1/2) ×(1-1/3×1/3) ×(1-1/4×1/4) ×…×(1-1/100×1/100)
问几道数学思考题⑴62又80/89×1/9⑵9又4/5+99又4/5+999又4/5+9999又4/5+4/5⑶2006
⑴62又80/89×1/9
=[63-9/89]*1/9
=63*1/9-9/89*1/9
=7-1/89
=6又80/89
⑵9又4/5+99又4/5+999又4/5+9999又4/5+4/5
=[9+99+999+9999]+4/5*5
=[10+100+1000+10000-4]+4
=11110
⑶2006÷2006又2006/2007
=2006/[2006(1+1/2007)]
=1/[2008/2007]
=2007/2008
⑷1×3+2×6+3×9+4×
12+5×15/1×2+2×4+3×6+4×8+5×10
=1*3[1+2*2+3*3+4*4+5*5]/[1*2(1+2*2+3*3+4*4+5*5]
=1*3/1*2
=3/2
⑸84又4/19×1.375+105又5/19×0.9
=2200/19+1800/19
=4000/19
⑹(1+1/2) ×(1-1/2) ×(1+1/3) ×(1-1/3) ×…×(1+1/100) ×(1-1/100)
=3/2*1/2*4/3*2/3*.*101/100*99/100
=1/2*101/100
=101/200
⑺(1-1/2×1/2) ×(1-1/3×1/3) ×(1-1/4×1/4) ×…×(1-1/100×1/100)
=[1-1/2][1+1/2][1-1/3][1+1/3].[1-1/10][1+1/10]
=1/2*3/2*2/3*4/3.9/10*11/10
=1/2*11/10
=11/20