求数学运算简便算法第一题:1/20+1/30+1/42+1/56+1/72+1/90=?第二题:12345679*72=?
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![求数学运算简便算法第一题:1/20+1/30+1/42+1/56+1/72+1/90=?第二题:12345679*72=?](/uploads/image/z/1244503-55-3.jpg?t=%E6%B1%82%E6%95%B0%E5%AD%A6%E8%BF%90%E7%AE%97%E7%AE%80%E4%BE%BF%E7%AE%97%E6%B3%95%E7%AC%AC%E4%B8%80%E9%A2%98%EF%BC%9A1%2F20%2B1%2F30%2B1%2F42%2B1%2F56%2B1%2F72%2B1%2F90%3D%3F%E7%AC%AC%E4%BA%8C%E9%A2%98%3A12345679%2A72%3D%3F)
求数学运算简便算法第一题:1/20+1/30+1/42+1/56+1/72+1/90=?第二题:12345679*72=?
求数学运算简便算法
第一题:1/20+1/30+1/42+1/56+1/72+1/90=?
第二题:12345679*72=?
求数学运算简便算法第一题:1/20+1/30+1/42+1/56+1/72+1/90=?第二题:12345679*72=?
1、原式=
(1/4)-(1/5)+(1/5)-(1/6)+(1/6)-(1/7)+(1/7)-(1/8)+(1/8)-(1/9)+(1/9)-(1/10)
=(1/4)-(1/10)
=3/20
2、12345679*72
=12345679*9*8
=111111111*8
=888888888
1、1/20+1/30+1/42+1/56+1/72+1/90
=1/(4*5)+1/(5*6)+1/(6*7)+1/(7*8)+1/(8*9)+1/(9*10)
=1/4-1/5+1/5-1/6+1/6-1/7+1/7-1/8+1/8-1/9+1/9-1/10
=1/4-1/10
=3/20
1、原式=1/4-1/5+1/5-1/6+1/6-1/7+1/7-1/8+1/8-1/9+1/9-1/10=1/4-1/10=0.15
2、计算器算阿- -就算前面的分解出来你还是要用计算器算。
1/20=1/4 - 1/5
1/30=1/5 - 1/6
.
.
.
1/90=1/9 - 1/10
原题=1/4 - 1/5 + 1/5 - 1/6 +....+ 1/9 - 1/10=1/4 - 1/10=3/20
(1/4)-(1/5)+(1/5)-(1/6)+(1/6)-(1/7)+(1/7)-(1/8)+(1/8)-(1/9)+(1/9)-(1/10) =(1/4)-(1/10) =3/20
12345679*72 =12345679*9*8 =111111111*8 =888888888