i don'n know

a)  A =1 /57

b)  B = 1/41

K MIK NHA

A = 1/57

B = 1/41

5 x (nhân)  (x + 3) - 17 = 23

= 5 x ( x + 3 ) = 23 + 17 = 40

= x + 3 = 40 : 5 = 8

x = 8 : 3

x = 2,6666.....

\(5\times(x+3)-17=23\)

\(\Rightarrow5\times(x+3)=23+17\)

\(\Rightarrow5\times(x+3)=40\)

\(\Rightarrow x+3=40\div5\)

\(\Rightarrow x+3=8\)

\(\Rightarrow x=8-3\)

\(\Rightarrow x=5\)

a) \(-\frac{1}{15}-\frac{1}{16}=-\frac{16}{240}-\frac{15}{240}=-\frac{31}{240}\)

b) \(\frac{7}{24}-\left(-\frac{5}{36}\right)=\frac{7}{24}+\frac{5}{36}=\frac{21}{72}+\frac{10}{72}=\frac{31}{72}\)

c) \(-\frac{7}{9}-\left(-\frac{7}{12}\right)=-\frac{7}{9}+\frac{7}{12}=-\frac{28}{36}+\frac{21}{36}=-\frac{7}{36}\)

\(a)\frac{-1}{15}-\frac{1}{16}\)

\(\frac{-1}{15}-\frac{1}{16}.MSC:240\)

\(=\frac{-1.16}{15.16}-\frac{1.15}{16.15}=\frac{-16}{240}-\frac{15}{240}=\frac{-16-15}{240}=\frac{-31}{240}\)

\(b)\frac{7}{24}-\frac{-5}{36}\)

\(\frac{7}{24}-\frac{-5}{36}.MSC:72\)

\(=\frac{7.3}{24.3}-\frac{-5.2}{36.2}=\frac{21}{72}-\frac{-10}{72}=\frac{21-\left(-10\right)}{72}=\frac{31}{72}\)

\(c)\frac{-7}{9}-\frac{-7}{12}\)

\(\frac{-7}{9}-\frac{-7}{12}.MSC:36\)

\(=\frac{-7.4}{9.4}-\frac{-7.3}{12.3}=\frac{-28}{36}-\frac{-21}{36}=\frac{-28-\left(-21\right)}{36}=\frac{-7}{36}\)

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    Nếu có gì sai thì báo lỗi cho mình biết nhé.

Bài làm

\(4\frac{1}{5}-\left(2\frac{3}{7}+8\frac{1}{5}\right)\)

\(=\frac{21}{5}-\left(\frac{17}{7}+\frac{41}{5}\right)\)

\(=\frac{147}{35}-\left(\frac{85}{35}+\frac{287}{35}\right)\)

\(=\frac{147-85-287}{35}=\frac{-225}{35}=-\frac{45}{7}\)

Đáp số là - \(\frac{45}{7}\)

Tìm hai số tự nhiên a và b biết: BCNN(a, b) = 1188;   ƯCLN(a, b) = 12.

\(\frac{12}{15}\)+  \(\frac{4}{5}\)= \(\frac{8}{5}\)