Phân tích thành nhân tử:
a/ xy(x+y) + yz(y+z) +zx(z+x) + 3xyz (tách 3xyz=xyz+xyz+xyz)
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Ta có :
A=xy(x+y+z) -xyz +(yz+zx)(x+y+z)
A=xy(x+y+z -z) + z(x+y)(x+y+z)
A=xy(x+y) +z(x+y)(x+y+z)
A=(x+y)(xy+z(x+y+z))
A=(x+y)(xy+zx+z(y+z))
A=(x+y)(x(y+z)+z(y+z))
A=(x+y)(y+z)(x+z)
P/ s : ko biết có đúng ko
Ta có
A=(x+y)(xy+yz+xz)+z(xy+yz+xz)-xyz
=(x+y)(xy+yz+xz)+xyz+z^2(y+x)-xyz
= (x+y)(xy+yz+xz + z^2)
= (x+y)(y+z)(x+z)
k cho mk đi
(xy+yz+zx)(x+y+z)-xyz
= (xy+yz)(x+y+z)+ x2z+xyz+ xz2-xyz
= (xy+yz)(x+y+z)+ x2z + xz2
= (x+z)(xy+y2+zy)+ xz(x+z) = (x+z)(xy+y2+zy+xz) = (x+z)(x+y)(x+z)
A=x2y+xy2+xyz+xyz+y2z+yz2+x2z+xyz+xz2-xyz
A=(x2y+xy2+xyz+y2z)+(yz2+x2z+xyz+xz2)
A=y(x2+xy+xz+yz)+z(yz+x2+xy+xz)
A=(y+z)(x2+xy+xz+yz)
A=(y+z)[x(x+y)+z(x+y)]
A=(y+z)(x+y)(x+z)
Ta có
C = xyz – (xy + yz + zx) + x + y + z – 1
= (xyz – xy) – (yz – y) – (zx – x) + (z – 1)
= xy(z – 1) – y(z – 1) – x(z – 1) + (z – 1)
= (z – 1)(xy – y – x + 1)
= (z – 1).[y(x – 1) – (x – 1)]
= (z – 1)(y – 1)(x – 1)
Với x = 9; y = 10; z = 101 ta có
C = (101 – 1)(10 – 1)(9 – 1) = 100.9.8 = 7200
Đáp án cần chọn là: C
\(=\dfrac{xy\left(z-1\right)-y\left(z-1\right)-x\left(z-1\right)+\left(z-1\right)}{xy\left(z+1\right)+y\left(z+1\right)-x\left(z+1\right)-\left(z+1\right)}\\ =\dfrac{\left(z-1\right)\left(xy-y-x+1\right)}{\left(z+1\right)\left(xy+y-x-1\right)}=\dfrac{\left(z-1\right)\left(x-1\right)\left(y-1\right)}{\left(z+1\right)\left(x+1\right)\left(y-1\right)}=\dfrac{\left(z-1\right)\left(x-1\right)}{\left(z+1\right)\left(x+1\right)}\\ =\dfrac{\left(5003-1\right)\left(5001-1\right)}{\left(5003+1\right)\left(5001+1\right)}=\dfrac{5002\cdot5000}{5004\cdot5002}=\dfrac{5000}{5004}=\dfrac{1250}{1251}\)
xy( x+ y) + yz(y+z) + xz(x+z) + 3xyz
= xy(x+y) + xyz + yz(y+z) + xyz + xz(x+z) + xyz
= zy(x+y+z) + yz(x + y + z) + xz ( x+y+z)
= ( x+ y +z )( xy + yz + zx)