phân tích đa thức thành nhân tử
a) x^7 + x^5 +1
b) x^8 + x^7 +1
c) x^8 + x^7 + 1
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\(=x^2\left(y+1\right)-\left(y+1\right)\)
=(y+1)(x-1)(x+1)
\(a,=4x^3\left(x+1\right)-x\left(x+1\right)=x\left(4x^2-1\right)\left(x+1\right)\\ =x\left(2x-1\right)\left(2x+1\right)\left(x+1\right)\\ b,=\left(a-1\right)^2-\left(b-c\right)^2\\ =\left(a-1-b+c\right)\left(a-1+b-c\right)\\ c,=\left(x^2-9x+14\right)\left(x^2-9x+20\right)-72\\ =\left(x^2-9x+17\right)^2-9-72\\ =\left(x^2-9x+17\right)^2-81=\left(x^2-9x+8\right)\left(x^2-9x+26\right)\\ =\left(x-1\right)\left(x-8\right)\left(x^2-9x+26\right)\)
a) x12 + 4 = x12 + 4x6 + 4 - 4x6 = (x6 + 2)2 - (2x3)2
= (x6 - 2x3 + 2)(x6 + 2x3 + 2)
b) 4x8 + 1 = 4x8 + 4x4 + 1 - 4x4 = (2x4 + 1)2 - (2x2)2
= (2x4 + 2x2 + 1)(2x4 - 2x2 + 1)
c) x7 + x5 - 1 = x7 - x + x5 + x2 - (x2 - x + 1) = x(x6 - 1) + x2(x3 + 1) - (x2 - x + 1)
= x(x3 - 1)(x3 + 1) + x2(x + 1)(x2 - x + 1) - (x2 - x + 1)
= (x4 - x)(x + 1)(x2 - x + 1) + (x3 + x2)(x2 - x + 1) - (x2 - x + 1)
= (x5 + x4 - x2 - x + x3 + x2 - 1)(x2 -x + 1)
= (x5 + x4 + x3 - x - 1)(x2 - x + 1)
d) x7 + x5 + 1 = x7 - x + x5 - x2 + (x2 + x + 1)
= x(x3 - 1)((x3 + 1) + x2(x3 - 1) + (x2 + x + 1)
= (x4 + x)(x - 1)(x2 + x + 1) + x2(x - 1)((x2 + x + 1) + (x2 + x + 1)
= (x2 + x + 1)(x5 - x4 + x2 - x + x3 - x2 + 1)
= (x2 + x + 1)(x5 - x4 + x3 - x + 1)
\(a,=\left(x-1\right)^4-2\left(x-1\right)^2+1\\ =\left[\left(x-1\right)^2-1\right]^2\\ =\left(x^2-2x-2\right)^2\\ b,=\left[\left(x+1\right)\left(x+5\right)\right]\left[\left(x+2\right)\left(x+4\right)\right]-4\\ =\left(x^2+6x+5\right)\left(x^2+6x+8\right)-4\\ =\left(x^2+6x\right)^2+13\left(x^2+6x\right)+36\\ =\left(x^2+6x+4\right)\left(x^2+6x+9\right)\\ =\left(x+3\right)^2\left(x^2+6x+4\right)\)
a) \(4\left(x+1\right)^3-x-1=4\left(x+1\right)^3-\left(x+1\right)=\left(x+1\right)\left[4\left(x+1\right)^2-1\right]=\left(x+1\right)\left[2\left(x+1\right)-1\right]\left[2\left(x+1\right)+1\right]=\left(x+1\right)\left(2x+1\right)\left(2x+3\right)\)
b) \(5x\left(x-3\right)+\left(3-x\right)^2-\left(x-3\right)=5x\left(x-3\right)+\left(x-3\right)^2-\left(x-3\right)=\left(x-3\right)\left(5x+x-3-1\right)=\left(x-3\right)\left(6x-4\right)=2\left(x-3\right)\left(3x-2\right)\)
c) \(9x^2y^3-3x^4y^2-6x^3y^2+16xy^4=xy^2\left(9xy-3x^3-6x^2+16y^2\right)\)