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\(x^8+3x^4+4\)
\(=\left(x^8-x^6+2x^4\right)+\left(x^6-x^4+2x^2\right)+\left(2x^4-2x^2+4\right)\)
\(=x^4\left(x^4-x^2+2\right)+x^2\left(x^4-x^2+2\right)+2\left(x^4-x^2+2\right)\)
\(=\left(x^4+x^2+2\right)\left(x^4-x^2+2\right)\)
\(4x^4+4x^3+5x^2+2x+1\)
\(=\left(4x^4+2x^3+2x^2\right)+\left(2x^3+x^2+x\right)+\left(2x^2+x+1\right)\)
\(=2x^2\left(2x^2+x+1\right)+x\left(2x^2+x+1\right)+\left(2x^2+x+1\right)\)
\(=\left(2x^2+x+1\right)^2\)
Đặt \(2x^2-x-2=t\)
Ta có:
\(A=\left(t+3\right)\left(t-3\right)+8\)
\(A=t^2-9+8\)
\(A=\left(t-1\right)\left(t+1\right)\)
Thay vào ta được:
\(A=\left(2x^2-x-3\right)\left(2x^2-x-1\right)\)
\(x^8+x^4-2\)
\(=\left(x^8-1\right)+\left(x^4-1\right)\)
\(=\left(x^4+1\right)\left(x^4-1\right)+\left(x^4-1\right)\)
\(=\left(x^4-1\right)\left(x^4+2\right)=\left(x^2-1\right)\left(x^2+1\right)\left(x^4+2\right)\)
câu b tớ thêm chút
a) x8+3x4+4
=x8-x4+4x4+4
=(x4-1)(x4+1)+4.(x4+1)
=(x4+1)(x4-1+4)
=(x4+1)(x4+3)
b) x6-x4-2x3+2x2
=x4.(x2-1)-2x2.(x-1)
=x4.(x-1)(x+1)-2x2(x-1)
=x2.(x-1)[x2(x+1)-2]
=x2.(x-1)(x3+x2-2)
=x2.(x-1)(x3-1+x2-1)
=x2.(x-1)[(x-1)(x2+x+1)+(x-1)(x+1)]
=x2.(x-1)(x-1)(x2+x+1+x+1)
=x2.(x-1)2.(x2+2x+2)
\(B=x^8+2x^5-2x^4+x^2-2x-100+10x\left(x^4+x\right)+\left(5x-1\right)^2\)
\(=x^8+2x^5-2x^4+x^2-2x-100+10x^5+25x^2-10x+1\)
\(=x^8+12x^5-2x^4+36x^2-12x-99\)
\(=x^8+6x^5+9x^4+6x^5+36x^2+54x-11x^4-66x-99\)
\(=x^4\left(x^4+6x+9\right)+6x\left(x^4+6x+9\right)-11\left(x^4+6x+9\right)\)
\(=\left(x^4+6x+9\right)\left(x^4+6x-11\right)\)
Đặt \(x^2-2x+4=a\)
Khi đó \(\left(x^2-2x+3\right)\left(x^2-2x+5\right)-8=\left(a-1\right)\left(a+1\right)-8\)
\(=a^2-1-8\)
\(=a^2-9\)
\(=\left(a-3\right)\left(a+3\right)\)
\(=\left(x^2-2x+4-3\right)\left(x^2-2x+4+3\right)\)
\(=\left(x^2-2x+1\right)\left(x^2-2x+7\right)\)
\(=\left(x-1\right)^2\left(x^2-2x+7\right)\)
Ta có : \(x^8+14x^4+1\)
\(=x^8+2.x^4.7+1\)
\(=x^8+2.x^4.7+49-48\)
\(=\left(x^4+7\right)^2-48\)
\(=\left(x^4+7-\sqrt{48}\right)\left(x^4+7+\sqrt{48}\right)\)
a/\(=\left(x^4+1\right)^2+12x^4=\left(x^4+1\right)^2+4x^2\left(x^4+1\right)+4x^4-4x^2\left(x^4+1\right)+8x^4\)
\(=\left(x^4+1+2x^2\right)^2-4x^2\left(x^4+1-2x^2\right)=\left(x^4+2x^2+1\right)-\left(2x^3-2x\right)^2\)
\(=\left(x^4+2x^3+2x^2-2x+1\right)\left(x^4-2x^3+2x^2+2x+1\right)\)
b/\(=\left(x^4+1\right)^2+96x^4=\left(x^4+1\right)^2+16x^2\left(x^4+1\right)+64x^4-16x^2\left(x^4+1\right)+32x^4\)
\(=\left(x^4+1+8x^2\right)^2-16x^2\left(x^4+1-2x^2\right)=\left(x^4+8x^2+1\right)-\left(4x^3-4x\right)^2\)
\(=\left(x^4+4x^3+8x^2-4x+1\right)\left(x^4-4x^3+8x^2+4x+1\right)\)
\(a,4x^4+4x^3-x^2-x=4x^3\left(x+1\right)-x\left(x+1\right)\)
\(=\left(x+1\right)\left(4x^3-x\right)\)
\(=x\left(x+1\right)\left(4x^2-1\right)\)
\(=x\left(x+1\right)\left(2x-1\right)\left(2x+1\right)\)
\(x^8+3x^4+4\)
\(=x^8+4x^4+4-x^4\)
\(=\left(x^4-2\right)^2-x^4\)
\(=\left(x^4-x^2-2\right)\left(x^4-x^2-2x^2-2\right)\)
\(=\left(x^2-2\right)\left(x^2+1\right)\left(x^2-1\right)\left(x^2+2\right)\)
\(=\left(x-1\right)\left(x+1\right)\left(x^2-2\right)\left(x^2+1\right)\left(x^2+2\right)\)
\(A=x^8-2x^4-8\)
\(A=x^8-2x^4+4x^4-8\)
\(A=x^4\left(x^4-2\right)-4\left(x^4-2\right)\)
\(A=\left(x^4-4\right)\left(x^4-2\right)\)
\(a=\left(x^2-2\right)\left(x^2+2\right)\left(x^4-2\right)\)
\(A=\left(x^4\right)^2-4x^4+2x^4-8\)
\(=x^4\left(x^4-4\right)+2\left(x^4-4\right)\)
\(=\left(x^4+2\right)\left(x^4-4\right)\)
\(=\left(x^4+2\right)\left(x^2+2\right)\left(x^2-2\right)\)
\(=\left(x^4+2\right)\left(x^2+2\right)\left(x-2\right)\left(x+2\right)\)
Bạn cũng có thể đặt \(t=x^4\)để bài toán dễ làm hơn