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1 + 2 + 3 + 4 + 5+ 6 + 7 + 8 + 9 = 45
lấy các số chẵn cộng lại vs nhau
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\(1+2+3+4+5+6+7+8+9\)
\(=\left(1+9\right)+\left(2+8\right)+\left(3+7\right)+\left(4+6\right)+5\)
\(=10+10+10+10+5\)
\(=10.4+5\)
\(=40+5\)
\(=45\)
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1+1+1+1+1=...?
2+2+2+2+2=...?
3+3+3+3+3=...?
4+4+4+4+4=4x5=20
5+5+5+5+5=5x5=25
6+6+6+6+6=6x5=30
7+7+7+7+7=7x5=35
8+8+8+8+8=8x5=40
9+9+9+9+9=9x5=45
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(3+7)+(4+6) +( 5+5)+(6+4)+(7+3)+(8+2)+(9+1)+(2+8)+(4+6)+(6+4)+(7+3)+(8+2)+(9+1)+(8+9)= 147
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2 = 1 + 1 6 = 2 + 4 8 = 5 + 3 10 = 8 + 2
3 = 1 + 2 6 = 3 + 3 8 = 4 + 4 10 = 7 + 3
4 = 3 + 1 7 = 1 + 6 9 = 8 + 1 10 = 6 + 4
4 = 2 + 2 7 = 5 + 2 9 = 6+ 3 10 = 5 + 5
5 = 4 + 1 7 = 4 + 3 9 = 7 + 2 10 = 10 + 0
5 = 3 + 2 8 = 7 + 1 9 = 5 + 4 10 = 0 + 10
6 = 5 + 1 8 = 6 + 2 10 = 9 + 1 1 = 1 + 0
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a) \(\frac{2}{9}+\frac{1}{5}+\frac{7}{9}+\frac{4}{5}=\left(\frac{2}{9}+\frac{7}{9}\right)+\left(\frac{1}{5}+\frac{4}{5}\right)= 1+1=2 \)
b) \(\frac{19}{37}+\left(1+\frac{19}{37}\right)=\left(\frac{19}{37}-\frac{19}{37}\right)+1=0+1=1\)
c) \(\frac{9}{8}-\left(\frac{17}{7}-\frac{3}{7}\right)+\frac{7}{8}=\frac{9}{8}+\frac{7}{8}-\left(\frac{17}{7}-\frac{3}{7}\right)=2-2=0\)
d) \(\frac{3}{5}\times\frac{8}{27}\times\frac{5}{3}=\frac{3}{5}\times\frac{5}{3}\times\frac{8}{27}=1\times\frac{8}{27}=\frac{8}{27}\)
e) \(\frac{7}{19}\times\frac{1}{3}+\frac{7}{19}\times\frac{2}{3}=\frac{7}{19}\times\left(\frac{1}{3}+\frac{2}{3}\right)=\frac{7}{19}\times1=\frac{7}{19}\)
f) \(\frac{12}{5}\times4-4\times\frac{7}{5}=4\times\left(\frac{12}{5}-\frac{7}{5}\right)=4\times1=4\)
1 + 2 + 3 + 4 + 5+ 6 + 7 + 8 + 9 = 45
Lấy các số chẵn cộng lại với nhau