Đề sai rồi bạn

\(\left\{{}\begin{matrix}\left(x+2\right)^2+\left(y-1\right)^2=x^2+y^2+7\left(1\right)\\\left(x+1\right)\left(y+2\right)=xy+5\left(2\right)\end{matrix}\right.\)

\(\left(2\right)\Leftrightarrow xy+2x+y+2=xy+5\Leftrightarrow2x+y+2=5\)

\(\Leftrightarrow y=3-2x\left(3\right)\)

\(\left(3\right)\left(1\right)\Rightarrow\left(x+2\right)^2+\left(2-2x\right)^2=x^2+\left(3-2x\right)^2+7\Rightarrow x=y=1\)

\(\left\{{}\begin{matrix}\dfrac{1}{x}+\dfrac{1}{y}=\dfrac{3}{4}\\\dfrac{1}{6x}+\dfrac{1}{5y}=\dfrac{2}{15}\end{matrix}\right.\)\(\left(x,y\ne0\right)\) \(đặt\left\{{}\begin{matrix}\dfrac{1}{x}=a\\\dfrac{1}{y}=b\end{matrix}\right.\)\(\Rightarrow\left\{{}\begin{matrix}a+b=\dfrac{3}{4}\\\dfrac{1}{6}a+\dfrac{1}{5}b=\dfrac{2}{15}\end{matrix}\right.\)

\(\Leftrightarrow\left\{{}\begin{matrix}a=\dfrac{1}{2}\\b=\dfrac{1}{4}\end{matrix}\right.\)\(\Leftrightarrow\left\{{}\begin{matrix}x=2\\y=4\end{matrix}\right.\)\(\left(tm\right)\)

a)Thời gian vật chuyển động: \(t=\sqrt{\dfrac{2h}{g}}=\sqrt{\dfrac{2\cdot80}{10}}=4s\)

b)Tốc độ vật khi vừa chạm đất là: \(v=v_0+gt=30+10\cdot4=70m/s\)

dễ

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