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a)B = ( 2 + 4 + 6 + 8 +........+ 2014 ) - ( 3 + 5 + 7 + 9 +.......+ 2011 )
= 1015056 - 1012035
= 3021
Mk nhanh nhất đó
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\(\frac{3}{5}\).\(\frac{-9}{13}\)+\(\frac{4}{13}\).\(\frac{-3}{5}\)+\(\frac{12}{7}\)=\(\frac{3}{5}\).\(\frac{-9}{13}\)+\(\frac{-4}{13}\).\(\frac{3}{5}\)+\(\frac{12}{7}\)
=\(\frac{3}{5}\).(\(\frac{-9}{13}\)+\(\frac{-4}{13}\))+\(\frac{12}{7}\)
= \(\frac{3}{5}\).-1+\(\frac{12}{7}\)
=\(\frac{-3}{5}\)+\(\frac{12}{7}\)
=\(\frac{39}{35}\)
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\(2.53.12+4.6.87-3.8.40\)
\(=2.53.4.3+4.6.87-3.2.4.40\)
\(=4.6.53+4.6.87-4.6.40\)
\(=4.6.\left(53+87-40\right)\)
\(=4.6.100=2400\)
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a) 1/2 + 3/4 - (3/4 - 4 - 5)
= 1/2 + 3/4 - 3/4 + 4 + 5
= (3/4 - 3/4) + (4 + 5) + 1/2
= 0 + 9 + 1/2
= 19/2
b) [9/16 + 8/(-27)] - (19/27- 7/16 - 2)
= 9/16 - 8/27 - 19/27 + 7/16 + 2
= (9/16 + 7/16) + (-8/27 - 19/27) + 2
= 1 - 1 + 2
= 2
c) -5/8 . [4/9 + 7/(-12)]
= -5/8 . (-5/36)
= 25/288
d) 7/10 . (-3/5) + 7/10 . (-2/5) - (-3/10)
= 7/10 . (-3/5 - 2/5) + 3/10
= 7/10 . (-1) + 3/10
= -2/5
e) -3/7 . 5/9 + 4/9 . (-3/7) + 2 3/7
= -3/7 . (5/9 + 4/9) + 17/7
= -3/7 . 1 + 17/7
= 2
f) 8 2/7 - (3 4/9 + 4 2/7)
= 8 + 2/7 - 3 - 4/9 - 4 - 2/7
= (8 - 3 - 4) + (2/7 - 2/7) - 4/9
= 1 - 4/9
= 5/9
h) 3.(-1/2)² - (4/5 + 8/15) : 5/6
= 3.1/4 - 4/3 : 5/6
= 3/4 - 8/5
= -17/20