Rút gọn rồi tính
\(\frac{8}{5}\)- \(\frac{18}{27}\)
\(\frac{12}{20}\)-\(\frac{6}{18}\)
\(\frac{8}{24}\)-\(\frac{5}{25}\)
\(\frac{18}{21}\)-\(\frac{12}{27}\)
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a) \(\frac{8}{5}-\frac{18}{27}=\frac{8}{5}-\frac{2}{3}\)
\(\Rightarrow\frac{8}{5}-\frac{2}{3}=\frac{24}{15}-\frac{10}{15}\)
\(\Rightarrow\frac{14}{15}\)
b) \(\frac{18}{21}-\frac{12}{27}=\frac{6}{7}-\frac{4}{9}\)
\(\Rightarrow\frac{6}{7}-\frac{4}{9}=\frac{54}{63}-\frac{28}{63}\)
\(\Rightarrow\frac{26}{63}\)
c) \(\frac{8}{24}-\frac{5}{25}=\frac{1}{3}-\frac{1}{5}\)
\(\Rightarrow\frac{1}{3}-\frac{1}{5}=\frac{5}{15}-\frac{3}{15}\)
\(\Rightarrow\frac{2}{15}\)
d) \(\frac{12}{20}-\frac{6}{18}=\frac{3}{5}-\frac{1}{3}\)
\(\Rightarrow\frac{3}{5}-\frac{1}{3}=\frac{9}{15}-\frac{5}{15}\)
\(\Rightarrow\frac{4}{15}\)
a) Ta có:
\(\begin{array}{l}\frac{{ - 10}}{{18}} =\frac{{ - 10:2}}{{18:2}} = \frac{{ - 5}}{9};\,\,\,\\\frac{{10}}{{18}} = \frac{{10:2}}{{18:2}} =\frac{5}{9};\,\,\\\,\frac{{15}}{{ - 27}} =\frac{{15:(-3)}}{{ - 27:(-3)}} = \frac{{ - 5}}{9};\,\\ - \frac{{20}}{{36}} =- \frac{{20:4}}{{36:4}}= \frac{{ - 5}}{9}.\end{array}\)
Vậy những phân số nào biểu diễn số hữu tỉ \(\frac{{ - 5}}{9}\) là: \(\frac{{ - 10}}{{18}};\,\frac{{15}}{{ - 27}};\, - \frac{{20}}{{36}}.\)
b) Số đối của các số \(12;\,\frac{{ 4}}{9};\, - 0,375;\,\frac{0}{5};\,-2\frac{2}{5}\) lần lượt là: \( - 12;\,\frac{-4}{9};\,0,375;\,\frac{0}{5};\, 2\frac{2}{5}\).
\(\frac{-63}{108}\)= \(\frac{-7}{12}\)
\(\frac{-33}{-77}\)= \(\frac{3}{7}\)
\(\frac{-5}{10}\)=\(\frac{-1}{2}\)
\(\frac{14}{63}\)=\(\frac{2}{9}\)
\(\frac{-15}{25}\)=\(\frac{-3}{5}\)
\(\frac{-45}{18}\)=\(\frac{-5}{2}\)
\(\frac{12}{15}\)=\(\frac{4}{5}\)
\(\frac{20}{25}\)=\(\frac{4}{5}\)
\(\frac{31}{12}\):Là phân số tối giản
t.i.c.k nha
\(B=\frac{9\sqrt{5}+3\sqrt{27}}{\sqrt{5}+\sqrt{3}}=\frac{9\sqrt{5}+9\sqrt{3}}{\sqrt{5}+\sqrt{3}}=\frac{9\left(\sqrt{5}+\sqrt{3}\right)}{\sqrt{5}+\sqrt{3}}=9\)
\(C=\frac{\sqrt{2}+\sqrt{3}+\sqrt{6}+\sqrt{8}+4}{\sqrt{2}+\sqrt{3}+\sqrt{4}}\)
\(=\frac{\sqrt{2}+\sqrt{3}+\sqrt{6}+\sqrt{8}+\sqrt{4}+\sqrt{4}}{\sqrt{2}+\sqrt{3}+\sqrt{4}}\)
\(=\frac{\left(\sqrt{2}+\sqrt{3}+\sqrt{4}\right)+\sqrt{2}.\left(\sqrt{2}+\sqrt{3}+\sqrt{4}\right)}{\sqrt{2}+\sqrt{3}+\sqrt{4}}\)
\(=\frac{\left(\sqrt{2}+\sqrt{3}+\sqrt{4}\right)\left(\sqrt{2}+1\right)}{\sqrt{2}+\sqrt{3}+\sqrt{4}}=\sqrt{2}+1\)
mik chỉnh lại đề
\(D=\frac{3\sqrt{8}-2\sqrt{12}+\sqrt{20}}{3\sqrt{18}-2\sqrt{27}+\sqrt{45}}=\frac{6\sqrt{2}-4\sqrt{3}+2\sqrt{5}}{9\sqrt{2}-6\sqrt{3}+3\sqrt{5}}\)
\(=\frac{2\left(3\sqrt{2}-2\sqrt{3}+\sqrt{5}\right)}{3\left(3\sqrt{2}-2\sqrt{3}+\sqrt{5}\right)}=\frac{2}{3}\)
\(\frac{8}{5}-\frac{18}{27}\)
\(=\frac{8}{5}-\frac{2}{3}\)
\(=\frac{24}{15}-\frac{10}{15}\)
\(=\frac{14}{15}\)
\(\frac{12}{20}-\frac{6}{18}\)
\(=\frac{3}{5}-\frac{1}{3}\)
\(=\frac{9}{15}-\frac{5}{15}\)
\(=\frac{4}{15}\)
\(\frac{8}{24}-\frac{5}{25}\)
\(=\frac{1}{3}-\frac{1}{5}\)
\(=\frac{5}{15}-\frac{3}{15}\)
\(=\frac{2}{15}\)
\(\frac{18}{21}-\frac{12}{27}\)
\(=\frac{6}{7}-\frac{4}{9}\)
\(=\frac{54}{63}-\frac{28}{63}\)
\(=\frac{26}{63}\)
1)8/5-2/3=14/15
2)3/5-1/3=4/15
3)1/3-1/5=2/15
4)6/7-4/9=26/63