1 + 1 = 2

Tk mk nha

1 + 1 = 2

Ai mk mk lại cho

\(y+\frac{1}{3}=\frac{7}{15}\div\frac{2}{5}\)

\(\Leftrightarrow y+\frac{1}{3}=\frac{7}{15}\times\frac{5}{2}\)

\(\Leftrightarrow y+\frac{2}{6}=\frac{7}{6}\)

\(\Leftrightarrow y=\frac{7}{6}-\frac{2}{6}\)

\(\Leftrightarrow y=\frac{5}{6}\)

\(y+\frac{1}{3}=\frac{7}{15}:\frac{2}{5}\)

\(y+\frac{1}{3}=\frac{7}{15}\times\frac{5}{2}\)

\(y+\frac{1}{3}=\frac{7}{6}\)

\(y=\frac{7}{6}-\frac{1}{3}\)

\(\Rightarrow y=\frac{5}{6}\)

Giả sử a=1;b=1 \(\Rightarrow\frac{1}{a}-\frac{1}{b}=\frac{1}{1}-\frac{1}{1}>2\)

\(\Rightarrow\) Đề sai.nếu đề là \(\frac{1}{a}+\frac{1}{b}\ge\frac{4}{a+b}\) thì:

\(\Leftrightarrow\frac{a+b}{ab}\ge\frac{4}{a+b}\)

\(\Leftrightarrow\left(a+b\right)^2\ge4ab\)

\(\Leftrightarrow\left(a-b\right)^2\ge0\)(*luôn đúng*)

Biết ngay là đề sai mà .

\(\frac{x}{2}\div\frac{1}{2}=\frac{1}{y}\)

\(\Leftrightarrow\frac{x}{2}\times\frac{2}{1}=\frac{1}{y}\)

\(\Leftrightarrow x=\frac{1}{y}\)

x/2.2=1/y

2x/2=1/y 

x=1/y 

suy ra xy=1

vi x thuoc Z va y khac 0 

suy ra x=-1;y=-1

hoac x=y=1

KL

\(A=\frac{15}{11}+\frac{5}{12}+\frac{11}{13}+\frac{9}{14}\)

\(\Rightarrow A=\left(1+\frac{4}{11}\right)+\left(1-\frac{7}{12}\right)+\left(1-\frac{2}{13}\right)+\left(1-\frac{5}{14}\right)\)

\(\Rightarrow A=\left(1+1+1+1\right)-\left(\frac{7}{12}-\frac{4}{11}+\frac{2}{13}+\frac{5}{14}\right)\)

\(\Rightarrow A=4-\left(\frac{7}{12}-\frac{4}{11}+\frac{2}{13}+\frac{5}{14}\right)< 4\)

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