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c ) − 5 15 = ( − 5 ) : 5 15 : 5 = − 1 2 d ) − 12 − 24 = ( − 12 ) : ( − 12 ) ( − 24 ) : ( − 12 ) = 1 2
e ) 54 270 = 54 : 54 270 : 54 = 1 5 f ) − 12 − 28 = ( − 12 ) : ( − 4 ) ( − 28 ) : ( − 4 ) = 3 7
g ) − 18 − 27 = ( − 18 ) : ( − 9 ) ( − 27 ) : ( − 9 ) = 2 3 h ) 45 − 24 = 45 : ( − 3 ) ( − 24 ) : ( − 3 ) = − 15 8
Tính các tổng dưới đây sau khi đã rút gọn phân số :
a)\(\dfrac{7}{21}\) + \(\dfrac{9}{-36}\) = \(\dfrac{7}{21}\)+\(\dfrac{-9}{36}\)=\(\dfrac{1}{3}\)+\(\dfrac{-1}{4}\)=\(\dfrac{4}{12}\)+\(\dfrac{-3}{12}\)=\(\dfrac{1}{12}\)
b) \(\dfrac{-12}{18}\)+\(\dfrac{-21}{35}\)=\(\dfrac{-2}{3}\)+\(\dfrac{-3}{5}\)=\(\dfrac{-10}{15}\)+\(\dfrac{-9}{15}\)=\(\dfrac{-19}{15}\)
c) \(\dfrac{-3}{21}\)+\(\dfrac{6}{42}\)=\(\dfrac{-1}{7}\)+\(\dfrac{1}{7}\)=0
d) \(\dfrac{-18}{24}\)+\(\dfrac{15}{-21}\)=\(\dfrac{-18}{24}\)+\(\dfrac{-15}{21}\)=\(\dfrac{-3}{4}\)+\(\dfrac{-5}{7}\)=\(\dfrac{-21}{28}\)+\(\dfrac{-20}{28}\)=\(\dfrac{-41}{28}\)
Bài 1: Tính
a) (−14) + (− 28) = -42 b) ( −26) + 47= 21 c) 35 + (− 63) = -28
d) ( −8) +12 +( −24)= -20 e) ( −26)−27= -53 f) ( −35)− ( −105)=70
Bài 2: Tính hợp lý
a) 54 +(12+ 46)= 112 b) 157− (200+57) =-100
c) (− 34) [(− 34)+2020]=(-34)+1986=1952
d) 45− (137− 155)=63 e) 27− 8− 12− 7 =0
f) ( −72)+26 −28− 6 =-80
a ) 1 3 b ) 1 4 c ) − 1 3
d ) 1 2 e ) 1 4 f ) 3 5
g ) 2 3 h ) − 3 2
a ) 7 21 + 9 36 = 1 3 + 1 4 = 4 12 + 3 12 = 7 12 ;
b ) 8 40 + − 36 45 = 1 5 + − 4 5 = − 3 5 ; c ) − 19 15 ; d ) − 41 28
a ) 73 84 ; b ) 1 7 ; c ) − 7 6 ; d ) 37 100