Cho B=\(\dfrac{n+1}{n-2}\) , Tìm n biết B= 4, B=\(\dfrac{-1}{2}\)
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1-3+5-7+9-11+.......+2021-2023
=(1-3)+(5-7)+(9-11)+...+(2021-2023)
=(-2)+(-2)+(-2)+....+(-2) (có 506 số -2)
=506 x (-2)
=-1012
Số gạo ban đầu: 44: (100% - 45%)= 80(kg)
Đ.số: 80 kg
\(6.3\\ \dfrac{8}{-11}=\dfrac{8.\left(-1\right)}{\left(-11\right).\left(-1\right)}=\dfrac{-8}{11};\dfrac{-5}{-9}=\dfrac{-5:\left(-1\right)}{\left(-9\right):\left(-1\right)}=\dfrac{5}{9}\\ --\\ 6.4\\ \dfrac{-12}{4}=\dfrac{-12:4}{4:4}=-3\\ \dfrac{7}{-35}=\dfrac{7:\left(-7\right)}{-35:\left(-7\right)}=-\dfrac{1}{5}\\ \dfrac{-9}{27}=\dfrac{-9:9}{27:9}=\dfrac{-1}{3}\)
\(6.5\\ 15p=\dfrac{15}{60}\left(h\right)=\dfrac{15:15}{60:15}\left(h\right)=\dfrac{1}{4}\left(h\right)\\ 90p=\dfrac{90}{60}\left(h\right)=\dfrac{90:30}{60:30}\left(h\right)=\dfrac{3}{2}\left(h\right)\)
a, Chiều cao thửa ruộng: 4800 x 2 : (50 + 60) = Số rất xấu em xem lại đề
\(A=\dfrac{1}{2}+\dfrac{1}{2^2}+\dfrac{1}{2^3}+...+\dfrac{1}{2^{2024}}\\ =>2A=1+\dfrac{1}{2}+\dfrac{1}{2^2}+...+\dfrac{1}{2^{2023}}\\ =>2A-A=A=1-\dfrac{1}{2^{2024}}=\dfrac{2^{2024}-1}{2^{2024}}\)
\(B=4\Rightarrow\dfrac{n+1}{n-2}=4\)
\(\Rightarrow n+1=4\left(n-2\right)\)
\(\Rightarrow n+1=4n-8\)
\(\Rightarrow4n-n=1+8\)
\(\Rightarrow3n=9\)
\(\Rightarrow n=3\)
b.
\(B=-\dfrac{1}{2}\Rightarrow\dfrac{n+1}{n-2}=-\dfrac{1}{2}\)
\(\Rightarrow n-2=-2\left(n+1\right)\)
\(\Rightarrow n-2=-2n-2\)
\(\Rightarrow n+2n=2-2\)
\(\Rightarrow3n=0\)
\(\Rightarrow n=0\)
\(B=4\\ \Leftrightarrow\dfrac{n+1}{n-2}=4\\ \Leftrightarrow4n+4=n-2\\ \Leftrightarrow4n-n=-2-4\\ \Leftrightarrow3n=-6\\ \Leftrightarrow n=-2\\ B=\dfrac{-1}{2}\\ \Leftrightarrow\dfrac{n+1}{n-2}=\dfrac{-1}{2}\\ \Leftrightarrow2n+2=-n+2\\ \Leftrightarrow2x+n=2-2\\ \Leftrightarrow3n=0\\ \Leftrightarrow n=0\)