2xy+4y^2+5x+10y
\(\text{2xy+4y^2+5x+10y}\)
Phân tích đa thức thành nhân tử
\(=2xy+5x+4y^2+10y\)
\(=x\left(2y+5\right)+2y\left(2y+5\right)\)
\(=\left(x+2y\right)\left(2y+5\right)\)
\(=2x\left(x+2y\right)+5\left(x+2y\right)=\left(x+2y\right)\left(2x+5\right)\)
X²-2xy+y²-25
X²-10x-y²+25
3x+3y+zx+zy
X²-4y²+5x+10y
Giải:
a) x2 - 2xy + y2 - 25 = (x - y)2 - 52 = (x - y - 5)(x - y + 5)
b) x2 - 10x - y2 + 25 = (x2 - 10x + 25) - y2 = (x - 5)2 - y2 = (x - 5 - y)(x - 5 + y)
c) 3x + 3y + zx + zy = (3x + 3y) + (zx + zy) = 3(x + y) + z(x + y) = (x + y)(3 + z)
d) x2 - 4y2 + 5x +10y = (x2 - 4y2) + (5x +10y) = (x - 2y)(x + 2y) + 5(x + 2y) = (x + 2y)(x - 2y + 5)
C=-x^2-10y^2-2xy-2x+4y-6
tìm giá trị lớn nhất của các biểu thức sau
\(D=-5x^2-4x-1\)
\(E=-x^2-4y^2+2xy+2x+10y-3\)
\(D=-5\left(x^2+\dfrac{4}{5}x+\dfrac{1}{5}\right)\)
\(=-5\left(x^2+2\cdot x\cdot\dfrac{2}{5}+\dfrac{4}{25}+\dfrac{1}{25}\right)\)
\(=-5\left(x+\dfrac{2}{5}\right)^2-\dfrac{1}{5}< =-\dfrac{1}{5}\)
Dấu = xảy ra khi x=-2/5
Tìm GTLN của:
\(A=-x^2+2xy-4y^2+2x+10y-3\)
Ta có \(A=-x^2+2xy-4y^2+2x+10y-3\)
\(A=-x^2+2\left(y+1\right)x-4y^2+10y-3\)
\(A=-x^2+2\left(y+1\right)x-\left(y+1\right)^2-3y^2+12y-2\)
\(A=-\left[x-\left(y+1\right)\right]^2-3\left(y^2-4y+4\right)+10\)
\(A=-\left(x-\left(y+1\right)\right)^2-3\left(y-2\right)^2+10\) \(\le10\)
Dấu "=" xảy ra \(\Leftrightarrow\left\{{}\begin{matrix}x=y+1\\y-2=0\end{matrix}\right.\Leftrightarrow\left(x,y\right)=\left(3,2\right)\)
Vậy \(max_A=10\)
Tìm giá trị lớn nhất của các biểu thức sau
A= \(-x^2\)+2xy\(-4y^2\) +2x +10y -3
B=\(-4x^2\)\(-5y^2\)+8xy+10y+12
\(A=-x^2+2xy-4y^2+2x+10y-3\)
\(=-x^2+2xy-y^2+2x-2y-1-3y^2+12y-12+10\)
\(=-\left(x^2-2xy+y^2-2x+2y+1\right)-3\left(y^2-4y+4\right)+10\)
\(=-\left(x-y-1\right)^2-3\left(y-2\right)^2+10< =10\)
Dấu '=' xảy ra khi \(\left\{{}\begin{matrix}x-y-1=0\\y-2=0\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}y=2\\x=y+1=3\end{matrix}\right.\)
\(B=-4x^2-5y^2+8xy+10y+12\)
\(=-4x^2+8xy-4y^2-y^2+10y-25+37\)
\(=-4\left(x^2-2xy+y^2\right)-\left(y^2-10y+25\right)+37\)
\(=-4\left(x-y\right)^2-\left(y-5\right)^2+37< =37\)
Dấu '=' xảy ra khi \(\left\{{}\begin{matrix}x-y=0\\y-5=0\end{matrix}\right.\)
=>x=y=5
tìm GTLN: -x^2+2xy-4y^2+2x+10y-8
\(A=-x^2+2xy-4y^2+2x+10y-8\)
\(=-\left(x^2-2xy+4y^2-2x-10y+8\right)\)
\(=-\left[\left(x-y-1\right)^2+3\left(y-2\right)^2-5\right]\)
\(=5-\left(x-y-1\right)^2-3\left(y-2\right)^2\le5\)
Dấu"=" xảy ra <=> \(\hept{\begin{cases}x-y-1=0\\y-2=0\end{cases}}\) <=> \(\hept{\begin{cases}x=3\\y=2\end{cases}}\)
Vậy MAX \(A=5\)khi \(x=3;\)\(y=2\)
Tìm GTLN C= -x^2 + 2xy - 4y^2 + 2x +10y -3
\(C=-x^2+2xy-4y^2+2x+10y-3\)
\(=-\left(x^2+2xy-y^2\right)+2x-2y-1-3y^2+12y-12+10\)
\(=-\left(x-y\right)^2+2\left(x-y\right)-1-3\left(y^2-4y+4\right)+10\)
\(=-\left(x-y-1\right)^2-3\left(y-2\right)^2+10\le10\forall x;y\)
Dấu "=" xảy ra \(\Leftrightarrow\hept{\begin{cases}x-y-1=0\\y-2=0\end{cases}\Leftrightarrow\hept{\begin{cases}x=3\\y=2\end{cases}}}\)
Vậy \(C_{max}=10\) tại x = 3; y = 2
tìm gtln của -x^2+2xy-4y^2+2x+10y-8
-x^2 + 2xy - 4y^2 + 2x + 10y - 8