Tính nhanh:
a) 2006 x 2005 - 1 / 2004 x 2006 + 2005
b) 18 x ( 19191919 / 21212121 + 88888 / 99999 )
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1, 2006 x 2005 - 1/2004 x 2006 + 2005 = 4411,202002
2,18 x (19191919/21212121 + 88888/99999) = 3,91015873
k mk nha pạn
mk nhanh nhất
= 18 x \(\left(\frac{19.1010101}{21.1010101}+\frac{8.11111}{9.11111}\right)\)= 18 x ( \(\frac{19}{21}+\frac{8}{9}\)) = 9 x 2 ( \(\frac{57+56}{63}\))
= 9 x 2 x \(\frac{113}{63}\)=\(\frac{226}{7}\)
\(\dfrac{2006\times2005-1}{2004\times2006+2005}=\dfrac{2006\times\left(2004+1\right)-1}{2004\times2006+2005}\)
\(=\dfrac{2004\times2006+2006-1}{2004\times2006+2005}=\dfrac{2004\times2006+2005}{2004\times2006+2005}\)
\(=1\)
\(18\times\left(\dfrac{19191919+88888}{21212121+99999}\right)=18\times\left(\dfrac{19}{21}+\dfrac{8}{9}\right)\)
\(=18\times\dfrac{113}{63}=\dfrac{226}{7}=32\dfrac{2}{7}\)
\(=18x\frac{19x1010101}{21x1010101}+\frac{8x11111}{9x11111}=18x\frac{19}{21}+\frac{8}{9}\)
\(18\left(\frac{19191919}{21212121}+\frac{88888}{99999}\right)\)
\(=18\left(\frac{19}{21}+\frac{8}{9}\right)\)
\(=18\left(\frac{57}{63}+\frac{56}{63}\right)\)
\(=18\left(\frac{113}{63}\right)\)
\(=\frac{3^2.2.113}{3^2.7}\)
\(=\frac{226}{7}\)
\(=18x\left(\frac{19}{21}+\frac{8}{9}\right)\)
\(=18x\frac{113}{63}\)
\(=\frac{226}{7}\)
\(=18\times\left(\frac{19}{21}+\frac{8}{9}\right)=18\times\frac{113}{63}=\frac{226}{7}\)
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