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\(C=x^2\left(x^2+x+1\right)-2x\left(x^2+x+1\right)+3\left(x^2+x+1\right)\)
\(=\left(x^2+x+1\right)\left(x^2-2x+3\right)\)
4x^2 - 7x -2 = 4x^2 - 8x + x - 2 = 4x(x - 2) + (x - 2) = (x -2)(4x + 1)
A=x14+x7+1
=(x14+x13+x12)-(x13+x12+x11)+(x11+x10+x9)-(x10+x9+x8)+(x8+x7+x6)-(x6+x5+x4)+(x5+x4+x3)-(x3+x2+x)+(x2+x+1)
Đặt B=x2+x+1
=>A=x12B-x11B+x9B-x8B+x6B-x4B+x3B-xB+B
=>A=B(x12-x11+x9-x8+x6-x4+x3-x+1)
Thay B=x2+x+1 vào A là xong
a) x4 + 2x3 + x2
= x2 ( x2 + 2x + 1 )
= x2 ( x + 1 )2
b) 5x2 - 10xy + 5y2 - 20z2
= 5 [(x2 - 2xy + y2 ) - 4z2 ]
= 5 [( x - y )2 - ( 2z )2 ]
= 5 ( x - y - 2z ) ( x - y + 2z )
c) x3 - x + 3x2y + 3xy2+ y3- y
= ( x3 + 3x2y + 3xy2 + y3 ) - ( x + y )
= (x + y )3 - ( x + y)
= ( x + y ) [( x + y )2 - 1 ]
= ( x + y ) ( x + y + 1 ) ( x + y - 1 )
\(a^4+a^2-2\)
\(=a^4-a^3+a^3-a^2+2a^2-2a+2a-2\)
\(=a^3\left(a-1\right)+a^2\left(a-1\right)+2a\left(a-1\right)+2\left(a-1\right)\)
\(=\left(a-1\right)\left(a^3+a^2+2a+2\right)\)
\(=\left(a-1\right)\left[a^2\left(a+1\right)+2\left(a+1\right)\right]\)
\(=\left(a-1\right)\left(a+1\right)\left(a^2+2\right)\)
\(x^4+2x^2-3\\ =\left(x^4-x^2\right)+\left(3x^2-3\right)\\ =x^2\left(x^2-1\right)+3\left(x^2-1\right)\\ =\left(x^2-1\right)\left(x^2+3\right)\\ =\left(x-1\right)\left(x+1\right)\left(x^2+3\right)\)
\(x^4+2x^2-3\)
\(=x^4+3x^2-x^2-3\)
\(=x^2\left(x^2+3\right)-\left(x^2+3\right)=\left(x^2+3\right)\left(x^2-1\right)\)
\(=\left(x^2+3\right)\left(x-1\right)\left(x+1\right)\)