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77/99=77:11/99:11=7/9
777/999=777:111/999:111=7/9
Vậy 7/9=77/99=777/999
77/99=77:11/99:11=7/9
777/999=777:111/999:111=7/9
Vậy 7/9=77/99=777/999
\(\dfrac{7}{9}=\dfrac{7}{9}\)
\(\dfrac{77}{99}=\dfrac{77\div11}{99\div11}=\dfrac{7}{9}\)
\(\dfrac{777}{999}=\dfrac{777\div111}{999\div111}=\dfrac{7}{9}\)
\(\dfrac{7777}{9999}=\dfrac{7777\div1111}{9999\div1111}=\dfrac{7}{9}\)
\(\Rightarrow\dfrac{7}{9}=\dfrac{77}{99}=\dfrac{777}{999}=\dfrac{7777}{9999}\)
\(\dfrac{77}{99}\) = \(\dfrac{77:11}{99:11}\) = \(\dfrac{7}{9}\)
\(\dfrac{777}{999}\) = \(\dfrac{777:111}{999:111}\) = \(\dfrac{7}{9}\)
\(\dfrac{7777}{9999}\) = \(\dfrac{7777:1111}{9999:1111}\) = \(\dfrac{7}{9}\)
Từ những lập luận luận trên ta có:
\(\dfrac{7}{9}\) = \(\dfrac{77}{99}\) = \(\dfrac{777}{999}\) = \(\dfrac{7777}{9999}\) (đpcm)
1+1+100000+1+1+1+1+9+999+1+1000+111+77+99+1=
\(1+1+100000+1+1+1+1+9+999+1+1000+111+77+99+1\)
\(=\left(999+1\right)+\left(99+1\right)+\left(9+1\right)+100000+\left(1+1+1+1+1\right)+77+111\)
\(=1000+100+10+5+77+111+100000\)
\(=1110+5+188+100000\)
\(=101110+5+188\)
\(=101115+188\)
\(=101303\)
99 + 426 - 942 + 999
= ( 999 - 99 ) + ( 942 - 426 )
= 100 + 516
= 616
HT
99+426-942+999=582
chắc vậy