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\(\left(\frac{5}{13}+\frac{8}{13}\right)+\left(\frac{-20}{41}+\frac{-21}{41}\right)+\frac{-5}{7}\)
\(=1+\left(-1\right)+\frac{-5}{7}\)
\(=\left(1-1\right)+\frac{-5}{7}\)
\(=0+\frac{-5}{7}\)
\(=\frac{-5}{7}\)
\(\frac{5}{13}+\left(-\frac{5}{7}\right)+\left(-\frac{20}{41}\right)+\frac{8}{13}+\left(-\frac{21}{41}\right)\)
\(=\left(\frac{5}{13}+\frac{8}{13}\right)+\left(-\frac{20}{41}+\frac{-21}{41}\right)+\left(-\frac{5}{7}\right)\)
\(=1+\left(-1\right)+\left(-\frac{5}{7}\right)\)
\(=0+\left(-\frac{5}{7}\right)=-\frac{5}{7}\)
6 phần 13 nhân 8 phần 7 nhân âm 26 phần 3 nhân âm 7 phần 8 = 4
\(\frac{3}{4}+\frac{-1}{3}+\frac{-5}{18}\)
\(=\frac{5}{12}+\frac{-5}{18}\)
\(=\frac{5}{36}\)
13/30+(-1)/5=13/30+(-6)/30=7/30
2/21+1/28=8/84+3/84=11/84
*Dấu phân số đc thay bởi dấu /
13 phần 30 + âm 1 phần 5 =7 phần 30
2 phần 21 + 1 phần 28 =11 phần 84
\(=\dfrac{10}{17}-\dfrac{5}{3}+7-\dfrac{8}{13}+\dfrac{11}{25}\)
\(=\dfrac{30}{51}-\dfrac{85}{51}+\dfrac{175}{25}+\dfrac{11}{25}-\dfrac{8}{13}\)
\(=\dfrac{-55}{51}+\dfrac{186}{25}-\dfrac{8}{13}\)
\(=\dfrac{-55\cdot325+186\cdot663-8\cdot1275}{16575}=\dfrac{95243}{16575}\)
1: Rút gọn
a) \(-\dfrac{33}{51}=\dfrac{-33:3}{51:3}=\dfrac{-11}{17}\)
b) \(\dfrac{156}{-168}=\dfrac{-156}{168}=\dfrac{-156:12}{168:12}=\dfrac{-13}{14}\)
c) \(\dfrac{-75}{-100}=\dfrac{75}{100}=\dfrac{75:25}{100:25}=\dfrac{3}{4}\)
2: Quy đồng mẫu:
a) \(-\dfrac{3}{8}\) và \(\dfrac{5}{4}\)
MSC: 8
\(-\dfrac{3}{8}=\dfrac{-3}{8}\)
\(\dfrac{5}{4}=\dfrac{5\cdot2}{4\cdot2}=\dfrac{10}{8}\)
b) \(\dfrac{-7}{6}\) ; \(\dfrac{5}{12}\) và \(-\dfrac{5}{6}\)
MSC: 12
\(-\dfrac{7}{6}=\dfrac{-7\cdot2}{6\cdot2}=\dfrac{-14}{12}\)
\(\dfrac{5}{12}=\dfrac{5}{12}\)
\(\dfrac{-5}{6}=\dfrac{-5\cdot2}{6\cdot2}=\dfrac{-10}{12}\)
\(\dfrac{5}{13}+\dfrac{-5}{7}+\dfrac{-20}{41}+\dfrac{8}{13}+\dfrac{-21}{41}\\ =\left(\dfrac{5}{13}+\dfrac{8}{13}\right)-\dfrac{5}{7}+\left(-\dfrac{20}{41}-\dfrac{21}{41}\right)\\ =1-\dfrac{5}{7}-1\\ =-\dfrac{5}{7}\)