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đa thức trên không thể phân tích dù tớ đã vào Cốc Cốc mà cốc cốc cũng bó tay
1.
a. x3 - 4x2 - xy2 + 4x
= x ( x2 - 4x + 4 - y2 )
= x [ ( x - 2 )2 - y2 ]
= x ( x - y - 2 ) ( x + y - 2 )
b. x2 - x - 2 = x2 + x - 2x - 2 = x ( x + 1 ) - 2 ( x + 1 ) = ( x - 2 ) ( x + 1 )
c. x4 + 4
= ( x4 + 2x3 + 2x2 ) - ( 2x3 + 4x2 + 4x ) + ( 2x2 + 4x + 4 )
= x2 ( x2 + 2x + 2 ) - 2x ( x2 + 2x + 2 ) + 2 ( x2 + 2x + 2 )
= ( x2 + 2x + 2 ) ( x2 - 2x + 2 )
\(x^8+3x^4+4\)
\(=\left(x^8-x^6+2x^4\right)+\left(x^6-x^4+2x^2\right)+\left(2x^4-2x^2+4\right)\)
\(=x^4\left(x^4-x^2+2\right)+x^2\left(x^4-x^2+2\right)+2\left(x^4-x^2+2\right)\)
\(=\left(x^4+x^2+2\right)\left(x^4-x^2+2\right)\)
\(4x^4+4x^3+5x^2+2x+1\)
\(=\left(4x^4+2x^3+2x^2\right)+\left(2x^3+x^2+x\right)+\left(2x^2+x+1\right)\)
\(=2x^2\left(2x^2+x+1\right)+x\left(2x^2+x+1\right)+\left(2x^2+x+1\right)\)
\(=\left(2x^2+x+1\right)^2\)
a/ x4 +5x3 +10x-4
=(x4- 4)+(5x3 + 10x)
=(x2+2) (x2-2) + 5x(x2 +2 )
=(x2+2)(x2 -2 +5x)
b/x5 - x4 +x3 -x2 +x-1
=x4(x-1)+x3(x-1)+(x-1)
=(x-1)(x4+x3+1)
\(x^5+x^4-x^3+x^2-x+2\)
\(=x^5+2x^4-x^4+2x^3-x^3+2x^2-x^2+2x-x+2\)
\(=x^4\left(x-2\right)-x^3\left(x-2\right)-x^2\left(x-2\right)-x\left(x-2\right)-\left(x-2\right)\)
\(=\left(x-2\right)\left(x^4-x^3-x^2-x-1\right)\)
Đặt \(A=\left(x-2\right)\left(x-4\right)\left(x-5\right)\left(x-10\right)-54x^2\)
\(=\left[\left(x-2\right)\left(x-10\right)\right]\left[\left(x-4\right)\left(x-5\right)\right]-54x^2\)
\(=\left(x^2-12x+20\right)\left(x^2-9x+20\right)-54x^2\)
Đặt \(x^2-12x+20=t\)
Khi đó: \(A=t\left(t+3x\right)-54x^2\)
\(=t^2+3tx-54x^2\)
\(=t\left(t-6x\right)+9x\left(t-6x\right)\)
\(=\left(t-6x\right)\left(t+9x\right)\)
\(=\left(x^2-18x+20\right)\left(x^2-3x+20\right)\)
Đặt A=\(\left(x+3\right)^4+\left(x+5\right)^4-2\)
\(=\left\lbrack\left(x+4\right)-1\right\rbrack^4+\left\lbrack\left(x+4\right)+1\right\rbrack^4-2\)
Đặt b=x+4
=>\(A=\left(b-1\right)^4+\left(b+1\right)^4-2\)
\(=\left(b^2-2b+1\right)^2+\left(b^2+2b+1\right)^2-2\)
\(=\left(b^2+1\right)^2-4b\left(b^2+1\right)+4b^2+\left(b^2+1\right)^2+4b\left(b^2+1\right)+4b^2-2\)
\(=2\left(b^2+1\right)^2+8b^2-2\)
\(=2\left\lbrack\left(b^2+1\right)^2+4b^2-1\right\rbrack\)
\(=2\cdot\left\lbrack b^4+2b^2+1+4b^2-1\right\rbrack=2\left(b^4+6b^2\right)=2b^2\left(b^2+6\right)\)
\(=2\left(x+4\right)^2\left\lbrack\left(x+4\right)^2+6\right\rbrack\)
cảm ơn bạn nhé