Bài 1:Tính:
a,-2/5-(-3/11)
b,(-5-1/2):1/2
Bài 2:Tính hợp lí nhất:
a,A=(2/3.1/4-1/3.1/2):(2/7.3/9-2/7.3/5)
b,B=(-4/5+5/7):2/3+(-1/3+2/7):2/3
Bài 3:Tính:
a,A=1/-2+1/-6+1/-12+1/-20+1/-30+1/-42+1/-56
Bài 1:Tính: a,-2/5-(-3/11) b,(-5-1/2):1/2 Bài 2:Tính hợp lí nhất: a,A=(2/3.1/4-1/3.1/2):(2/7.3/9-2/7.3/5) b,B=(-4/5+5/7):2/3+(-1/3+2/7):2/3 Bài 3:Tính
By Rose
Đáp án:
Bài 1 :
$a) -\dfrac{2}{5} – (-\dfrac{3}{11})$
$ = -\dfrac{2}{5} + \dfrac{3}{11}$
$ = \dfrac{22}{55} + \dfrac{15}{55}$
$ = \dfrac{37}{55}$
$b) (-5 – \dfrac{1}{2}) : \dfrac{1}{2}$
$ =(\dfrac{-10}{2} – \dfrac{1}{2}) : \dfrac{1}{2}$
$ = \dfrac{-11}{2} : \dfrac{1}{2}$
$ =-11$
Bài 2 :
$a, A = (\dfrac{2}{3} . \dfrac{1}{4} – \dfrac{1}{3} . \dfrac{1}{2} ) : (\dfrac{2}{7} . \dfrac{3}{9} – \dfrac{2}{7} .\dfrac{3}{5})$
$ A = (\dfrac{1}{6} -\dfrac{1}{6}) : ( \dfrac{2}{7} – (\dfrac{3}{9} – \dfrac{3}{5})$
$ A = 0 : ( \dfrac{2}{7} – \dfrac{4}{15})$
$ A = 0$
$b, B = (-\dfrac{4}{5} +\dfrac{5}{7} : \dfrac{2}{3} + (-\dfrac{1}{3} +\dfrac{2}{7}) : \dfrac{2}{3}$
$ B = (\dfrac{2}{7} + \dfrac{5}{7}) : \dfrac{2}{3} + (-\dfrac{1}{3} -\dfrac{4}{5}) : \dfrac{2}{3}$
$ B = 1 : \dfrac{2}{3} – \dfrac{17}{15} : \dfrac{2}{3}$
$ B = \dfrac{3}{2} – \dfrac{17}{10}$
$ B = -\dfrac{1}{5}$
Bài 3 :
$A = \dfrac{1}{-2} + \dfrac{1}{-6} + \dfrac{1}{-12} + \dfrac{1}{-20} + \dfrac{1}{-30} + \dfrac{1}{-42} +\dfrac{1}{-56}$
$A = -(\dfrac{1}{2} + \dfrac{1}{6} + \dfrac{1}{12} + \dfrac{1}{20} +\dfrac{1}{30} +\dfrac{1}{42} +\dfrac{1}{56})$
$A = – (1 -\dfrac{1}{2} + \dfrac{1}{2} – \dfrac{1}{3} + \dfrac{1}{3} – \dfrac{1}{4} +\dfrac{1}{4} -\dfrac{1}{5}+\dfrac{1}{5} -\dfrac{1}{6} +\dfrac{1}{6} -\dfrac{1}{7} +\dfrac{1}{7} -\dfrac{1}{8})$
$ A = -(1 – \dfrac{1}{8})$
$ A = – (\dfrac{8}{8} – \dfrac{1}{8})$
$ A = – (\dfrac{7}{8})$
$ = -\dfrac{7}{8}$
Đáp án:
bài 1
a) -2/5 – (-3/11)
= -2/5 + 3/11
= -22/55 + 15/55
= -7/55
b) (-5 – 1/2) : 1/2
= (-10/2 – 1/2) : 1/2
= -11/2 : 1/2
= -11
( sorry bn, do mik cx vội nên chỉ có thể làm đc bài 1 )