Question

[Kar day]

23h hạn chót mn giúp em vs

Answer 1

[Nguyễn Lê Phước Thịnh]

Câu 3: 

b: Áp dụng tính chất của dãy tỉ số bằng nhau, ta được:

\(\dfrac{a}{2}=\dfrac{b}{3}=\dfrac{c}{4}=\dfrac{2a-b+3c}{2\cdot2-3+3\cdot4}=\dfrac{39}{13}=3\)

Do đó: a=6; b=9; c=12

Answer 2

[Nguyễn Tân Vương]

\(\text{1)Thực hiện phép tính(tính nhanh nếu có thể):}\)

\(\text{a)}\dfrac{5}{21}-1\dfrac{1}{7}+\dfrac{4}{3}\)             \(\text{b)}\dfrac{12}{25}+\dfrac{27}{13}+\dfrac{13}{25}-\dfrac{40}{13}-0,25\)

\(=\dfrac{5}{21}+\dfrac{-8}{7}+\dfrac{4}{3}\)           \(=\dfrac{12}{25}+\dfrac{27}{13}+\dfrac{13}{25}+\left(\dfrac{-40}{13}\right)+\left(\dfrac{-1}{4}\right)\)

\(=\left(\dfrac{-19}{21}\right)+\dfrac{4}{3}\)             \(=\left(\dfrac{12}{25}+\dfrac{13}{25}\right)+\left(\dfrac{27}{13}+\dfrac{-40}{13}\right)+\left(\dfrac{-1}{4}\right)\)

\(=\dfrac{3}{7}\)                               \(=1+\left(-1\right)+\left(\dfrac{-1}{4}\right)\)

                                      \(=0+\left(\dfrac{-1}{4}\right)=\dfrac{-1}{4}\)

\(\text{c)}1,6.\sqrt{100}+9:\left(\dfrac{-3}{2}\right)^3-\left(\dfrac{2019}{2020}\right)^0\)

\(=\dfrac{8}{5}.10+9:\dfrac{27}{8}-1\)

\(=16+\dfrac{8}{3}-1\)

\(=\dfrac{56}{3}-1=\dfrac{53}{3}\)

\(\text{2)Tìm x,biết:}\)

\(\text{a)}1\dfrac{2}{5}+x=\dfrac{11}{5}\)                              \(\text{b)}\dfrac{1}{5}x-1\dfrac{2}{3}=\dfrac{4}{3}\)

\(\dfrac{7}{5}+x=\dfrac{11}{5}\)                                       \(\dfrac{1}{5}x\)           \(=\dfrac{4}{3}+\dfrac{5}{3}=\dfrac{9}{3}=3\)

        \(x=\dfrac{11}{5}+\left(\dfrac{-7}{11}\right)=\dfrac{86}{55}\)                \(x\)           \(=3.5=15\)

\(\text{c)}\left|x-\dfrac{1}{2}\right|=\dfrac{3}{5}\)

\(\text{Vậy x-}\dfrac{1}{2}=\dfrac{3}{5}\)

       \(x\)      \(=\dfrac{3}{5}+\left(\dfrac{-1}{2}\right)=\dfrac{1}{10}\)

\(\text{hoặc x-}\dfrac{1}{2}=\left(\dfrac{-3}{5}\right)\)

         \(x\)     \(=\left(\dfrac{-3}{5}\right)+\left(\dfrac{-1}{2}\right)=\dfrac{-11}{10}\)

\(\Rightarrow x\in\left\{\dfrac{1}{10};\left(\dfrac{-11}{10}\right)\right\}\)

\(\text{3)f}\left(\dfrac{-1}{2}\right)=\dfrac{1}{2}-3.\left(\dfrac{-1}{2}\right)=\dfrac{1}{2}-\left(\dfrac{-3}{2}\right)=2\)

\(f\left(\dfrac{1}{6}\right)=\dfrac{1}{2}-3.\dfrac{1}{6}=\dfrac{1}{2}-\dfrac{1}{2}=0\)

\(\text{b)Áp dụng tính chất dãy tỉ số bằng nhau:}\)

           \(\dfrac{a}{2}=\dfrac{b}{3}=\dfrac{c}{4}=\dfrac{2a-b+3c}{2.3-3+3.4}=\dfrac{39}{13}=3\)

\(\Rightarrow a=3.2=6\)

\(b=3.3=9\)

\(c=3.4=12\)

Câu 4 mik ko biết làm,bn thông cảm:(((