Pt đa thức thành NT :
câu 15 : -x mũ 2 + 6x + 6y + y mũ 2
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1) \(x^2+6y-9-y^2=x^2-\left(y^2-6y+9\right)=x^2-\left(y-3\right)^2=\left(x-y+3\right)\left(x+y-3\right)\)
2) \(9y^2-6y+1-25x^2=\left(3y\right)^2-2.3y+1-\left(5x\right)^2=\left(3y-1\right)^2-\left(5x\right)^2\)
\(=\left(3y-1-5x\right)\left(3y-1+5x\right)\)
3) \(a^2-9+6x-x^2=a^2-\left(x^2-6x+9\right)=a^2-\left(x-3\right)^2=\left(a-x+3\right)\left(a+x-3\right)\)
\(x^2-y^2+z^2-t^2-2xz+2yt=\)
\(=\left(x^2-2xz+z^2\right)-\left(y^2-2yt+t^2\right)=\)
\(=\left(x-z\right)^2-\left(y-t\right)^2=\)
\(=\left[\left(x-z\right)-\left(y-t\right)\right]\left[\left(x-z\right)+\left(y-t\right)\right]\)
\(x^2-y^2+z^2-t^2-2xz+2yt\)
\(=\left(x^2-2xz+z^2\right)-\left(y^2+2yt+t^2\right)\)
\(=\left(x-z\right)^2-\left(y-t\right)^2\)
\(=\left(x-z+y-t\right)\times\left(x-z-y+t\right)\)
\(1,a^2-2a+1-b^2\)
\(=\left(a^2-2a+1\right)-b^2\)
\(=\left(a-1\right)^2-b^2\)
\(=\left(a-1-b\right)\left(a-1+b\right)\) Khai triển thành hằng đẳng thức số 3 e nhé.
\(2,x^2+2xy+y^2-81\)
\(=\left(x^2+2xy+y^2\right)-81\)
\(=\left(x+y\right)^2-9^2\)
\(=\left(x+y-9\right)\left(x+y+9\right)\)Cái này cũng HĐT số 3 nè
\(3,x^2+6y-9-y^2\)
\(=-\left(y^2-6y+9\right)+x^2\)
\(=-\left(y-3\right)^2+x^2\)
\(=x^2-\left(y-3\right)^2\)
\(=\left(x-y-3\right)\left(x-y+3\right)\)
\(5,4x^2+y^2-9-4xy\)
\(=\left(4x^2-4xy+y^2\right)-9\)
\(=\left(2x-y\right)^2-3^2\)
\(=\left(2x-y-3\right)\left(2x-y+3\right)\)
Học tốt
\(a,x^2+7x+7y-y^2\)
\(=x^2-y^2+7\left(x+y\right)\)
\(=\left(x-y\right)\left(x+y\right)+7\left(x+y\right)\)
\(=\left(x+y\right)\left(x-y+7\right)\)
\(b,x^2-2x-9y^2+6y\)
\(=x^2-\left(3y\right)^2-2\left(x-3y\right)\)
\(=\left(x-3y\right)\left(x+3y\right)-2\left(x-3y\right)\)
\(=\left(x-3y\right)\left(x+3y-2\right)\)
\(c,x^2-xy+x^3-3x^{2y}+3x^{2y}-y^3\)
\(=x\left(x-y\right)+\left(x-y\right)\left(x^2+xy+y^2\right)\)
\(=\left(x-y\right)\left(x+x^2+xy+y^2\right)\)
\(-x^2+6x+6y+y^2\\=-(x^2-6x+9)+(y^2+6y+9)\\=-(x-3)^2+(y+3)^2\\=(y+3)^2-(x-3)^2\\=[(y+3)-(x-3)][(y+3)+(x-3)]\\=(y+3-x+3)(y+3+x-3)\\=(y-x+6)(x+y)\)