842 nha bn

là 842 nha bn

\(x+y+z=1\Rightarrow z=1-x-y\)Thay vào A ta được:

\(A=2xy+3y\left(1-x-y\right)+4\left(1-x-y\right)x\)

\(\Leftrightarrow2xy+3y-3xy-3y^2+4x-4x^2-4xy-A=0\)

\(\Leftrightarrow3y-3y^2+4x-4x^2-5xy-A=0\)

\(\Leftrightarrow-4x^2-\left(5y-4\right)x-3y^2+3y-A=0\)

\(\Leftrightarrow4x^2+\left(5y-4\right)x+3y^2-3y+A=0\)

\(\Delta=\left(5y-4\right)^2-16\left(3y^2-3y+A\right)\)

Để pt có nghiệm \(\Leftrightarrow\Delta\ge0\)

\(\Leftrightarrow\left(5y-4\right)^2-16\left(3y^2-3y+A\right)\ge0\)

\(\Leftrightarrow25y^2-40y+16-48y^2+48y-16A\ge0\)

\(\Leftrightarrow-23y^2+8y+16\ge16A\)

\(\Leftrightarrow16A\le-23\left(y^2-\frac{8}{23}y-\frac{12}{23}\right)=-23\left(y-\frac{4}{23}\right)^2+\frac{384}{23}\le\frac{384}{23}\)

\(\Rightarrow A\le\frac{24}{23}\)

Dấu "=" xảy ra \(\Leftrightarrow\hept{\begin{cases}2xy+3y\left(1-x-y\right)+4\left(1-x-y\right)x=\frac{24}{23}\\\left(y-\frac{4}{23}\right)^2=0\\x+y+z=1\end{cases}}\)

\(\Leftrightarrow\hept{\begin{cases}x=\frac{9}{23}\\y=\frac{4}{23}\\z=\frac{10}{23}\end{cases}}\)

Vậy Max A = \(\frac{24}{23}\)\(\Leftrightarrow\hept{\begin{cases}x=\frac{9}{23}\\y=\frac{4}{23}\\z=\frac{10}{23}\end{cases}}\)

Bạn viết rõ đề ra đi.

giải cho mình pt này:
$\text{3x-13\sqrt{\text{x +6}}}$

           \(\frac{3}{1.3}+\frac{3}{3.5}+\frac{3}{5.7}+....+\frac{3}{99.101}\)

\(=\frac{3}{2}\left(1-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+...+\frac{1}{99}-\frac{1}{101}\right)\)

\(=\frac{3}{2}\left(1-\frac{1}{101}\right)\)

\(=\frac{3}{2}.\frac{100}{101}\)

\(=\frac{150}{101}\)

Đặt A=\(\frac{3}{1.3}+\frac{3}{3.5}+\frac{3}{5.7}+...+\frac{3}{99.101}\)

\(\frac{1}{2}A=\frac{1}{2}\left(\frac{3}{1.3}+\frac{3}{3.5}+...+\frac{3}{99.101}\right)\)

\(\frac{1}{2}A=\frac{2}{1.3}+\frac{2}{3.5}+...+\frac{2}{99.101}\)

\(\frac{1}{2}A=1-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+...+\frac{1}{99}-\frac{1}{101}\)

\(\frac{1}{2}A=1-\frac{1}{101}\)

\(\frac{1}{2}A=\frac{100}{101}\)

\(A=\frac{100}{101}:\frac{1}{2}\)

\(A=\frac{200}{101}\)

\(\left(5-2\sqrt{6}\right)^{\frac{x}{2}}+\left(5+2\sqrt{6}\right)^{\frac{x}{2}}=10\)

\(pt\Leftrightarrow\sqrt{\left(\sqrt{3}-\sqrt{2}\right)^{2x}}+\sqrt{\left(\sqrt{3}+\sqrt{2}\right)^{2x}}=10\)

\(\Leftrightarrow\left(\sqrt{3}-\sqrt{2}\right)^x+\left(\sqrt{3}+\sqrt{2}\right)^x=10\)

\(\Leftrightarrow\frac{1}{\left(\sqrt{3}+\sqrt{2}\right)^x}+\left(\sqrt{3}+\sqrt{2}\right)^x=10\)

\(\Leftrightarrow\frac{1}{t}+t=10\left(t=\left(\sqrt{3}+\sqrt{2}\right)^x\right)\)

\(\Leftrightarrow t^2-10t+1=0\)\(\Leftrightarrow t=5\pm2\sqrt{6}\)

\(\Rightarrow5\pm2\sqrt{6}=\left(\sqrt{3}+\sqrt{2}\right)^x\)

\(\Leftrightarrow\left(\sqrt{3}+\sqrt{2}\right)^{\pm2}=\left(\sqrt{3}+\sqrt{2}\right)^x\)

\(\Rightarrow x=\pm2\). Vậy...

câu này nghĩa là : anh 1 đi không trở lại để lại mình em với thằng bé

ko hỉu ???

ngu chó bài dỡ ẹt mà kg biết hihihi

\(5x^2-22x+23=0\)

\(\Leftrightarrow25x^2-110x+115=0\)

\(\Leftrightarrow\left(5x\right)^2-2.5x.11+121=6\)

\(\Leftrightarrow\left(5x-11\right)^2=6\)

\(\Leftrightarrow5x-11=\pm\sqrt{6}\)

\(\Leftrightarrow x=\frac{11\pm\sqrt{6}}{5}\)

Vậy...