xy(x+y)+yz(y+z)+xz(x+z)+2xyz
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3(x-3)(x+7)+(x-4)2+48
=3(x2+7x-3x-21)+(x2-8x+16)+48
=3x2+21x-9x-63+x2-8x+16+48
=3x2+x2+21x-9x-8x-63+16+48
=4x2+4x+64
=4(x2+x+16)
Ta thay x=0,5 vào đa thức :
=4(0,52+0,5+16)
=4.16,75
=67
![](https://rs.olm.vn/images/avt/0.png?1311)
ta có: x2+y2+z2+2x-4y+6z+14=0
(x2+2x+1)+(y2-4y+4)+(z2+6z+9)=0
(x+1)2+(y-2)2+(z+3)2=0
=> x = -1; y = 2; z = -3
vậy x+y+z =-2
![](https://rs.olm.vn/images/avt/0.png?1311)
1)
\(y=x^2+5x-4\)
\(=x^2+2.x.\frac{5}{2}+\frac{25}{4}-\left(\frac{25}{4}+4\right)\)
\(=\left(x+\frac{5}{2}\right)^2-10,25\)
\(Min_y=-10,25\Leftrightarrow x=-\frac{5}{2}\)
2) \(y=2x^2-6x+5\)
\(=2\left(x^2-2.x.\frac{3}{2}+\frac{9}{4}\right)+\frac{1}{2}\)
\(=2\left(x-\frac{3}{2}\right)^2+\frac{1}{2}\)
\(Min_y=\frac{1}{2}\Leftrightarrow x=\frac{3}{2}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
1
(x2-8)2+36
=x4-16x2+64+36
=x4+20x2+100-36x2
=(x2+10)2-(6x)2
HĐT số 3
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1
x2-y2-x+y
=(x-y)(x+y)-(x-y)
=(x-y)(x+y-1)
2
b(1-a)-x(1-a3)
=(1-a)-x(1-a)(1+a+a2)
=(1-a)(1-x-ax-xa2)
3
x4+4x2-5
=x4+4x2+4-9
=(x2+2)2_32
=(x2+2-3)(x2+2+3)
=(x2-1)(x2+5)
c6
4a2b2-(a2+b2-c2)2
=(2ab)2-(a2+b2-c2)2
=(2ab-a2-b2+c2)(2ab+a2+b2-c2)
![](https://rs.olm.vn/images/avt/0.png?1311)
c1:
x3+3x2+3x+1-27z3
=(x+1)3-(3z)3
=(x+1-3z)[(x+1)2-(x+1)3z+9z2)
=(x+1-3z)(x2+2x+1-3xz-3z+9x2)
c2:
x2-2xy+y2-xz+yz
=(x-y)2-z(x-y)
=(x-y)(x-y-z)
\(xy\left(x+y\right)+yz\left(y+z\right)+xz\left(x+z\right)+2xyz\)
\(=x^2y+xy^2+y^2z+yz^2+x^2z+xz^2+2xyz\)
\(\text{Chúc bạn học tốt \!}\)
\(\text{Nếu đúng thì tích nha !}\)
xy(x+y)+yz(y+z)+xz(x+z)+2xyz
=x2y+xy2+y2x+yz2+x2z+xz2+2xyz
=> hết biết làm