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a) \(x^3-\dfrac{1}{9}x=0\)
\(\Rightarrow x\left(x^2-\dfrac{1}{9}\right)=0\)
\(\Rightarrow x\left(x-\dfrac{1}{3}\right)\left(x+\dfrac{1}{3}\right)=0\)
\(\Rightarrow\left[{}\begin{matrix}x=0\\x-\dfrac{1}{3}=0\Leftrightarrow x=\dfrac{1}{3}\\x+\dfrac{1}{3}=0\Leftrightarrow x=-\dfrac{1}{3}\end{matrix}\right.\)
b) \(x\left(x-3\right)+x-3=0\)
\(\Rightarrow\left(x-3\right)\left(x+1\right)=0\)
\(\Rightarrow\left[{}\begin{matrix}x-3=0\Rightarrow x=3\\x+1=0\Rightarrow x=-1\end{matrix}\right.\)
c) \(2x-2y-x^2+2xy-y^2=0\) (thêm đề)
\(\Rightarrow2\left(x-y\right)-\left(x-y\right)^2=0\)
\(\Rightarrow\left(x-y\right)\left(2-x+y\right)=0\)
\(\Rightarrow\left\{{}\begin{matrix}x-y=0\Rightarrow x=y\\2-x+y=0\Rightarrow x-y=2\end{matrix}\right.\)
\(\Rightarrow\left\{{}\begin{matrix}x=y\left(1\right)\\\left(1\right)\Rightarrow x-x=2\left(loại\right)\end{matrix}\right.\)
d) \(x^2\left(x-3\right)+27-9x=0\)
\(\Rightarrow x^2\left(x-3\right)+\left(x-3\right).9=0\)
\(\Rightarrow\left(x-3\right)\left(x^2+9\right)=0\)
\(\Rightarrow x-3=0\Rightarrow x=3.\)
Bài 1:
a, \(2x\left(y-z\right)+5y\left(z-y\right)=2x\left(y-z\right)-5y\left(y-z\right)\)
\(=\left(y-z\right)\left(2x-5y\right)\)
b, \(x^3-3x^2+3x-1=x^3-x^2-2x^2+2x+x-1\)
\(=x^2.\left(x-1\right)-2x.\left(x-1\right)+\left(x-1\right)\)
\(=\left(x-1\right)\left(x^2-2x+1\right)=\left(x-1\right)\left(x^2-x-x+1\right)\)
\(=\left(x-1\right)\left(x-1\right)^2=\left(x-1\right)^3\)
c, \(7x^2-7xy-4x+4y=7x.\left(x-y\right)-4.\left(x-y\right)\)
\(=\left(x-y\right)\left(7x-4\right)\)
d, \(x^2-6x+8=x^2-2x-4x+8\)
\(=x.\left(x-2\right)-4\left(x-2\right)=\left(x-2\right)\left(x-4\right)\)
Chúc bạn học tốt!!!
1)
a) \(2x\left(y-z\right)+5y\left(z-y\right)\)
\(=2x\left(y-z\right)-5y\left(y-z\right)\)
\(=\left(y-z\right)\left(2x-5y\right)\)
b) \(x^3-3x^2+3x-1\)
\(=x^3-3.x^2.1+3.x.1^2-1^3\)
\(=\left(x-1\right)^3\)
c) \(7x^2-7xy-4x+4y\)
\(=7x\left(x-y\right)-4\left(x-y\right)\)
\(=\left(x-y\right)\left(7x-4\right)\)
d) \(x^2-6x+8\)
\(=x^2-4x-2x+8\)
\(=x\left(x-4\right)-2\left(x-4\right)\)
\(=\left(x-4\right)\left(x-2\right)\)
2)
a) \(\left(5x^2+3x-1\right)\left(x+3\right)\)
\(=5x^3+3x^2-x+15x^2+9x-3\)
\(=5x^3+3x^2+15x^2-x+9x-3\)
\(=5x^3+18x^2+8x-3\)
b) \(\left(x^3+2x^2+3x-1\right):\left(x^2-2\right)\)
\(=x+2+\dfrac{5x+3}{x^2-2}\)
Ta có: (a2 + b2)(x2 + y2) = (ax + by)2
<=> a2x2 + a2y2 + b2x2 + b2y2 = a2x2 + 2axby + b2y2
<=> a2x2 + a2y2 + b2x2 + b2y2 - a2x2 - 2axby - b2y2 = 0
<=> (a2y2 - axby) + (b2x2 - axby) = 0
<=> ay(ay - bx) - bx(ay - bx) = 0
<=> (ay - bx)2 = 0
<=> ay - bx = 0
Vậy bài toán đã được chứng minh
Sửa đề: thì \(ay-bx=0\)
Giải:
Xét hiệu: \(\left(a^2+b^2\right)\left(x^2+y^2\right)-\left(ax+by\right)^2\)
\(=a^2x^2+a^2y^2+b^2x^2+b^2y^2-a^2x^2-b^2y^2\) \(-2axby\)
\(=a^2y^2-2axby+b^2x^2\)
\(=\left(ay-bx\right)^2=0\Leftrightarrow ay-bx=0\) (Đpcm)
\(\text{a) }\left(\dfrac{1}{2}a^2x^4+\dfrac{4}{3}\:ax^3-\dfrac{2}{3}ax^2\right):\left(-\dfrac{2}{3}\:ax^2\right)\\ =-3ax^2-2x+1\)
\(\text{b) }4\left(\dfrac{3}{4}x-1\right)+\left(12x^2-3x\right):\left(-3x\right)-\left(2x+1\right)\\ =3x-4-4x+1-2x-1\\ =-3x-4\)
kết quả cuối cùng là: a. -\(\dfrac{3}{4}ax^2-2x+1\)
b. \(\)-\(3x-4\)
\(\left(a+b+c\right)^3-\left(a-b-c\right)^3-6a\left(b+c\right)^2\)
\(=a^3+3a^2\left(b+c\right)+3a\left(b+c\right)^2+\left(b+c\right)^3-\left[a^3-3a^2\left(b+c\right)+3a\left(b+c\right)^2-\left(b+c\right)^3\right]-6a\left(b+c\right)^2\)
\(=a^3+3a^2\left(b+c\right)+3a\left(b+c\right)^2+\left(b+c\right)^3-a^3+3a^2\left(b+c\right)-3a\left(b+c\right)^2+\left(b+c\right)^3-6a\left(b+c\right)^2\)
\(=2\left(b+c\right)^3-6a\left(b+c\right)^2+6a^2\left(b+c\right)\)
\(=\left(b+c\right)\left(2b^2+4bc+2c^2-6ab-6ac+6a^2\right)\)
\(=2\left(b+c\right)\left(b^2+2bc+c^2-3ab-3ac+3a^2\right)\)
\(P=5x^2-4xy+8x+y^2+17\)
\(P=4x^2-4xy+y^2+x^2+8x+16+1\)
\(P=\left(2x-y\right)^2+\left(x+4\right)^2+1\)
Vậy: MinP là 1 khi x=-4, y=-8
\(\left(x+y+z\right)^2-2\left(x+y+z\right)\left(x+y\right)+\left(x+y\right)^2\)
= \(\left[\left(x+y+z\right)-\left(x+y\right)\right]^2\)
= \(z^2\)
Ta có:(x + y + z)2 - 2(x + y + z) (x + y) + (x + y)2
=[(x+y+z)-(x+y)]2=z2
a,(5x-2y)(x2-xy+1)=5x3-5x2+5x-2yx2+2xy2-2y
=5x3-7x2y+2xy2+5x-2y
b,(x-2)(x+2)(\(\dfrac{1}{2}\) x-5)=x2-4.\(\left(\dfrac{1}{2}x-5\right)\)
=\(\dfrac{1}{2}x^3-5x^2-2x+20\)
c,\(\left(x^2-2x+3\right)\left(\dfrac{1}{2}x-5\right)\)
=\(\dfrac{1}{2}x^3-5x^2-1x^2+10x+\dfrac{3}{2}x-15\)
=\(\dfrac{1}{2}x^3-6x^2+\dfrac{23}{2}x-15\)
d,\(\left(x^2-5\right)\left(x+3\right)+\left(x+4\right)\left(x-x^2\right)\)
=\(x^3+3x^2-5x-15+x^2-x^3+4x-4x^2\)
=\(-5x+4x-15\)
=\(-x-15\)
Chúc bạn học tốt(mỏi tay quá)