Tính hợp lí: –5/8×2/19–5/8×17/19
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\(\dfrac{4}{5}\)+\(\dfrac{-5}{4}\)=\(\dfrac{0}{4}\)
\(\dfrac{-1}{3}\)+\(\dfrac{2}{5}-\dfrac{5}{6}\)=\(\dfrac{-10}{30}+\dfrac{12}{30}-\dfrac{25}{30}\)=\(\dfrac{-23}{30}\)
\(\dfrac{2}{3}-\dfrac{5}{7}.\dfrac{14}{25}\)=\(\dfrac{2}{3}-\dfrac{2}{5}\)=\(\dfrac{10}{15}-\dfrac{6}{15}\)=\(\dfrac{4}{15}\)
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\(=\dfrac{8}{23}+\dfrac{3}{19}-\dfrac{15}{17}-\dfrac{2}{17}+\dfrac{15}{23}=\dfrac{3}{19}\)
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\(\left(\dfrac{8}{23}+\dfrac{3}{19}-\dfrac{15}{17}\right)-\left(\dfrac{2}{17}-\dfrac{15}{23}\right)\\ =\dfrac{8}{23}+\dfrac{3}{19}-\dfrac{15}{17}-\dfrac{2}{17}+\dfrac{15}{23}\\ =\left(\dfrac{8}{23}+\dfrac{15}{23}\right)-\left(\dfrac{15}{17}+\dfrac{2}{17}\right)+\dfrac{3}{19}\\ =1-1+\dfrac{3}{19}\\ =\dfrac{3}{19}\)
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A = ( -4/5 + 4/3 ) + (-5/4 + 14/5) - 7/3
= 8/15 + 31/20 - 7/3
= 25/12 - 7/3
= -1/4
B = 8/3 x 2/5 x 3/8 x 10x 19/92
= 16/15 x 15/4 x 19/92
= 4x19/92
= 19/23
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a) \(-\frac{4}{15}\cdot\left(-\frac{3}{8}\right)\cdot\left(\frac{15}{-4}\right)\cdot8\)
\(=\left(-\frac{4}{15}\cdot\left(\frac{15}{-4}\right)\right)\cdot\left(-\frac{3}{8}\cdot8\right)\)
\(=1\cdot\left(-3\right)=-3\)
b) \(-\frac{2}{3}\cdot\frac{4}{19}+\frac{5}{3}\cdot\frac{4}{19}\)
\(=\frac{4}{19}\cdot\left(\frac{5}{3}-\frac{2}{3}\right)\)
\(=\frac{4}{19}\cdot1=\frac{4}{19}\)
c) \(-\frac{1}{2}\cdot\frac{5 }{3}+\frac{1}{2}\cdot\frac{8}{3}\)
\(=\frac{1}{2}\left(\frac{8}{3}-\frac{5}{3}\right)\)
\(=\frac{1}{2}\cdot1=\frac{1}{2}\)
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1) 125.(-24) + 24.225.
\(=24\left(-125+225\right)=24.100=2400.\)
2) 512.(2 – 128) – 128. (-512).
\(=512\left(2-128+128\right)=512.2=1024.\)
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\(a.\frac{1}{2}+\frac{7}{8}+\frac{17}{19}+\frac{42}{47}< 1+1+1+1\)
\(< 4\)
\(b.\frac{3}{2}+\frac{6}{5}+\frac{17}{11}+\frac{197}{193}>1+1+1+1\)
\(>4\)
Ủng hộ mk nha ^_-
a)Ta có:
1/2<1 7/8<1 17/19<1 42/47<1
Vậy:
1/2+7/8+17/19+42/47<1+1+1+1(do từng số hạng trong vế trái đều nhỏ hơn từng số hạng bên vế phải)
Vậy: 1/2+7/8+17/19+42/47<4
b)Ta có:
3/2>1 6/5>1 17/11>1 197/193>1
Vậy:
3/2+6/5+17/11+197/193>1+1+1+1
Vậy 3/2+6/5+17/11+197/193>4
Chúc em học tốt^^
\(-\dfrac{5}{8}\times\dfrac{2}{19}-\dfrac{5}{8}\times\dfrac{17}{19}\\ =-\dfrac{5}{8}\times\left(\dfrac{2}{19}+\dfrac{17}{19}\right)\\ =-\dfrac{5}{8}\times1\\ =-\dfrac{5}{8}.\)