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\(A=x\left(y^2-z^2\right)+y\left(z^2-x^2\right)+z\left(x^2-y^2\right)=x\left(y^2-z^2\right)+y\left(-y^2+z^2-x^2+y^2\right)+z\left(x^2-y^2\right)=\left(y^2-z^2\right)\left(x-y\right)+\left(x^2-y^2\right)\left(z-y\right)=\left(y-z\right)\left(y+z\right)\left(x-y\right)-\left(x-y\right)\left(x+y\right)\left(y-z\right)=\left(x-y\right)\left(y-z\right)\left(y+z-x-y\right)=\left(x-y\right)\left(y-z\right)\left(z-x\right)\)
\(B=a\left(b^3-c^3\right)+b\left(c^3-a^3\right)+c\left(a^3-b^3\right)=ab^3-ac^3+bc^3-a^3b+a^3c-b^3c=ab\left(b^2-a^2\right)-c^3\left(a-b\right)+c\left(a^3-b^3\right)=-ab\left(a-b\right)\left(a+b\right)-c^3\left(a-b\right)+c\left(a-b\right)\left(a^2+ab+b^2\right)=\left(a-b\right)\left(-a^2b-ab^2-c^3+a^2c+abc+b^2c\right)\)
a(b3 - c3) + b(c3 - a3) + c(a3 - b3)
= a(b3 - c3 ) + b( c3 - b3 + b3 - a3) + c(a3 - b3)
= a(b3 - c3) + b(c3 - b3) + b(b3 - a3) + c(a3 - b3)
\(=\left[a\left(b^3-c^3\right)-b\left(b^3-c^3\right)\right]-\left[b\left(a^3-b^3\right)-c\left(a^3-b^3\right)\right]\)
= (b3 - c3)(a - b) - (a3- b3)(b - c)
= (b - c)(b2 + bc + c2)(a - b) - (a - b)(a2 + ab + b2)(b - c)
= (b - c)(a - b)(b2 + bc + c2 - a2 + ab - b2)
= (b - c)(a - b) [ (c2 - a2) + (bc - ab) ]
= (b - c)(a - b) [ (c - a)(c + a) + b(c - a) ]
= (b - c)(a -b) [ (c - a)(c + a + b) ]
= (a- b)(b - c)(c - a)(a + b + c)
a) \(x^4+2x^3-4x-4=\left(x^4+2x^3+x^2\right)-\left(x^2+4x+4\right)\)
\(=\left(x^2+x\right)^2-\left(x+2\right)^2=\left(x^2+x-x-2\right)\left(x^2+x+x+2\right)\)
\(=\left(x^2-2\right)\left(x^2+2x+2\right)\)
a) Ta có: \(x^4+2x^3-4x-4\)
\(=\left(x^4+2x^3+x^2\right)-\left(x^2+4x+4\right)\)
\(=\left(x^2+x\right)^2-\left(x+2\right)^2\)
\(=\left(x^2+x-x-2\right)\left(x^2+x+x+2\right)\)
\(=\left(x^2-2\right)\cdot\left(x^2+2x+2\right)\)
a(b3 - c3) + b(c3 - a3) + c(a3 - b3)
= a(b3 - c3 ) + b( c3 - b3 + b3 - a3) + c(a3 - b3)
= a(b3 - c3) + b(c3 - b3) + b(b3 - a3) + c(a3 - b3)
= a(b3 - c3) - b(b3 - c3) - [b(a3 - b3) - c(a3- b3)]
= (b3 - c3)(a - b) - (a3- b3)(b - c)
= (b - c)(b2 + bc + c2)(a - b) - (a - b)(a2 + ab + b2)(b - c)
= (b - c)(a - b)(b2 + bc + c2 - a2 + ab - b2)
= (b - c)(a - b) [ (c2 - a2) + (bc - ab) ]
= (b - c)(a - b) [ (c - a)(c + a) + b(c - a) ]
= (b - c)(a -b) [ (c - a)(c + a + b) ]
= (a- b)(b - c)(c - a)(a + b + c)
\(a\left(b^2+c^2\right)+b\left(a^2+c^2\right)+c\left(a^2+b^2\right)-2abc-a^3-b^3-c^3\)
\(=c\left(a-b\right)^2+\left[ab^2+ac^2+a^2b+bc^2-a^3-b^3-c^3\right]\)
\(=c\left(a-b\right)^2+c^2\left(a+b-c\right)+ab^2+a^2b-a^3-b^3\)
\(=c\left(a-b\right)^2+c^2\left(a+b-c\right)-\left(a^3-a^2b\right)+\left(ab^2-b^3\right)\)
\(=c\left(a-b\right)^2+c^2\left(a+b-c\right)-a^2\left(a-b\right)+b^2\left(a-b\right)\)
\(=c\left(a-b\right)^2+c^2\left(a+b-c\right)-\left(a+b\right)\left(a-b\right)^2\)
\(=-\left(a-b\right)^2\left(a+b-c\right)+c^2\left(a+b-c\right)\)
\(=\left(a+b-c\right)\left(a-b+c\right)\left(-a+b+c\right)\)
a) \(x^2+2x+1=x^2+x+x+1=x\left(x+1\right)+\left(x+1\right)=\left(x+1\right)\left(x+1\right)=\left(x+1\right)^2\) *Câu này có thể áp dụng hằng đẳng thức \(a^2+2ab+b^2=\left(a+b\right)^2\) cho nhanh*
b) \(a^3-b^3+c^3+3abc=\left(a^3-3a^2b+3ab^2-b^2\right)+3a^2b-3ab^2+c^3+3abc\)
\(=\left(a-b\right)^3+c^3+\left(3a^2b-3ab^2+3abc\right)\)
\(=\left(a-b+c\right)\left[\left(a-b\right)^2-\left(a-b\right)c+c^2\right]+3ab\left(a-b+c\right)\)
\(=\left(a-b+c\right)\left(a^2-2ab+b^2-ac+bc+c^2+3ab\right)\)
\(=\left(a-b+c\right)\left(a^2+b^2+c^2-ac+bc+ab\right)\)
c) \(a^3-b^3-c^3-3abc=\left[a^3-3a^2b+3ab^2-b^3\right]+3a^2b-3ab^2-c^3-3abc\)
\(=\left[\left(a-b\right)^3-c^3\right]+3ab\left(a-b-c\right)=\left(a-b-c\right)\left[\left(a-b\right)^2+\left(a-b\right)c+c^2\right]+3ab\left(a-b-c\right)\)
\(=\left(a-b-c\right)\left[a^2-2ab+b^2+ac-bc+c^2+3ab\right]=\left(a-b-c\right)\left(a^2+b^2+c^2+ab+ac-bc\right)\)
a,(x+1)2
b,(a+c-b).{(a+c)^2+(a+c)b+b^2-3ac}
c,(a-c-b).{(a-c)^2+(a-c)b+b^2+3ac}