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a: =(1-2-3+4)+(5-6-7+8)+...+(21-22-23+24)
=0+0+...+0
=0
b: =-7111+53+711-153=-6400-100=-6500
c: =-43(-1-296+296)=-43*(-1)=43

bài 1:
b) 47.69-31.(-47) = 47.69-(-31).47
= 47.(69 + 31)
= 47.100
= 4700
các bạn ơi giúp mình bài 2 với mình đang cần gấp nhanh mình tk cho thề

|-105|-|-25|+|15|-|5|
= 105 - 25 + 15 - 5
= 80 + 15 - 5
=95 - 5
= 90
53.(-7)+47.(-7)+14.(-25)-4.(-25)
=(-7).[47+53] + -25.(14-4)
= -7 . 100 + -25.10
=-700 + -250
=-950

a) -7/25 . 11/13 + -7/25 . 2/13 - 18/25=-1
b) 5/7 . 1/3 - 5/7 . 1/4 - 5/7 . 1/12=0
c) 5 + 2/5 . 4+ 2/7 + 5 + 5/7 . 5+ 2/5=18
d) 75% - 3/2 + 0,5 - [ -1/2]^2=-1/2

a) \(\dfrac{7}{-25}+\dfrac{8}{25}=\dfrac{-7}{25}+\dfrac{8}{25}=\dfrac{1}{25}\)
\(\dfrac{4}{5}+\dfrac{4}{-18}=\dfrac{4}{5+\left(-18\right)}=\dfrac{4}{-13}=\dfrac{-4}{13}\)
\(\dfrac{7}{21}+\dfrac{9}{-36}=\dfrac{1}{3}+\dfrac{1}{-4}=\dfrac{1}{3+\left(-4\right)}=\dfrac{1}{-1}=1\)
b) \(\dfrac{12}{20}-\dfrac{2}{5}=\dfrac{12}{20}+\left(\dfrac{-2}{5}\right)=\dfrac{3}{5}+\dfrac{-2}{5}=\dfrac{3+\left(-2\right)}{5}=\dfrac{1}{5}\)
\(\dfrac{2}{3}-\dfrac{-5}{6}=\dfrac{2}{3}+\dfrac{5}{6}=\dfrac{4}{6}+\dfrac{5}{6}=\dfrac{9}{6}=\dfrac{3}{2}\)
\(6-\dfrac{3}{20}=6+\dfrac{-3}{20}=\dfrac{60}{60}+\dfrac{-9}{60}=\dfrac{51}{60}\)
c) \(\dfrac{2}{21}.\dfrac{-7}{3}=\dfrac{2.\left(-1\right)}{7.3}=\dfrac{-2}{21}\)
\(\dfrac{27}{28}.\left(-21\right)=\dfrac{27.\left(-21\right)}{28}=\dfrac{-567}{28}\)
\(\dfrac{-15}{7}.\dfrac{-14}{25}=\dfrac{-3.\left(-2\right)}{1.5}=\dfrac{6}{5}\)

a)
7-x-25-7=-25
-x-25=-25
-x=0
x=0
b)
(3x-24).73=2.74
3x-24 = 2.74 : 73 = 2.74-3=2.7=14
3x-16=14
3x=14+16=30
x=30:3=10
(-4).2.6.25.(-7).25
=-100.50.-14
=-5000.-14
=70000