1. Tìm x,y,z
a) 7x+2+2.7x-1= 345
b)(x+z)x+2=(x-1)x+6 với x thuộc Z
c) I 2x-3I = 3-x
d) 2x=3y; 5y=7z và 3x-7y+5z=30
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\(1,\dfrac{x}{2}=\dfrac{y}{5}=\dfrac{x+y}{2+5}=\dfrac{21}{7}=3\\ \Rightarrow\left\{{}\begin{matrix}x=6\\y=15\end{matrix}\right.\\ 2,7x=3y\Rightarrow\dfrac{x}{3}=\dfrac{y}{7}=\dfrac{x-y}{3-7}=\dfrac{16}{-4}=-4\\ \Rightarrow\left\{{}\begin{matrix}x=-12\\y=-28\end{matrix}\right.\\ 3,\dfrac{x}{5}=\dfrac{y}{6}=\dfrac{z}{7}=\dfrac{x-y-z}{5-6-7}=\dfrac{36}{-8}=-\dfrac{9}{2}\\ \Rightarrow\left\{{}\begin{matrix}x=-\dfrac{45}{2}\\y=-27\\z=-\dfrac{63}{2}\end{matrix}\right.\\ 4,x:y:z=3:5:7\Rightarrow\dfrac{x}{3}=\dfrac{y}{5}=\dfrac{z}{7}=\dfrac{2x+3y-z}{6+15-7}=\dfrac{-14}{14}=-1\\ \Rightarrow\left\{{}\begin{matrix}x=-3\\y=-5\\z=-7\end{matrix}\right.\)
3. Áp dụng tính chất dãy tỉ số bằng nhau, ta có:
\(\dfrac{x}{5}=\dfrac{y}{6}=\dfrac{z}{7}=\dfrac{x-y-z}{5-6-7}=\dfrac{36}{-8}=\dfrac{-9}{2}\)
\(x=\dfrac{-45}{2}\)
\(y=-27\)
\(z=\dfrac{-63}{2}\)
Bài 4:
a: \(=7xy\left(2-3-4\right)=-35xy\)
b: \(=\left(x-5\right)\left(x+y\right)\)
c: \(=10x\left(x-y\right)+8\left(x-y\right)=2\left(x-y\right)\left(5x+4\right)\)
d: \(=\left(x+y\right)^3-\left(x+y\right)\)
=(x+y)(x+y+1)(x+y-1)
e: =x^2+8x-x-8
=(x+8)(x-1)
f: \(=2x^2-4x+x-2=\left(x-2\right)\left(2x+1\right)\)
g: =-5x^2+15x+x-3
=(x-3)(-5x+1)
h: =x^2-3xy+xy-3y^2
=x(x-3y)+y(x-3y)
=(x-3y)*(x+y)
Bài 4:
a: \(=7xy\left(2-3-4\right)=-35xy\)
b: \(=\left(x-5\right)\left(x+y\right)\)
c: \(=10x\left(x-y\right)+8\left(x-y\right)=2\left(x-y\right)\left(5x+4\right)\)
d: \(=\left(x+y\right)^3-\left(x+y\right)\)
=(x+y)(x+y+1)(x+y-1)
e: =x^2+8x-x-8
=(x+8)(x-1)
f: \(=2x^2-4x+x-2=\left(x-2\right)\left(2x+1\right)\)
g: =-5x^2+15x+x-3
=(x-3)(-5x+1)
h: =x^2-3xy+xy-3y^2
=x(x-3y)+y(x-3y)
=(x-3y)*(x+y)
1
2x . 3=3y .4
=> x=2y=>\(\frac{x}{2}=y\Rightarrow\frac{x}{4}=\frac{y}{2}\)
\(\frac{x}{4}=\frac{z}{5}\)
\(\Rightarrow\frac{x}{4}=\frac{y}{2}=\frac{z}{5}=\frac{x-2y+3z}{4-4+15}=\frac{1}{15}=\)
x=1/15x4=4/15
y=1/15x2=2/15
z=1/15x6=1/10
\(\Rightarrow x-y-z=\frac{4}{15}-\frac{2}{15}-\frac{1}{10}=\frac{1}{30}\)
\(\left(2x-3\right)^2-2\left(3x+1\right)^2=2x\left(x-2\right)+\left(x-1\right)\left(x+2\right)\)
4\(x^2\)-12x+9-2(9\(x^2\)+6x+1)=2\(x^2\)-4x+\(x^2\)+2x-x-2
4\(x^2\)-12x+9-18\(x^2\)-12x-2=2\(x^2\)-4x+\(x^2\)+2x-x-2
(4\(x^2\)-18\(x^2\)-2\(x^2\)-\(x^2\)) +(-12x-12x+4x-2x+x)+(9-2+2)=0
-17\(x^2\)-21x+9=0
Nguyễn Thanh Hằng Nhã Doanh ngonhuminh nguyen thi vang mấy ban giup mk voi
a) 3y +xy+2x+6=0
3.(y + 2) + x.(y + 2) = 0
(3 + x).(y + 2) = 0
\(\Rightarrow\hept{\begin{cases}3+x=0\\y+2=0\end{cases}\Rightarrow\hept{\begin{cases}x=-3\\y=-2\end{cases}}}\)
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