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Q = \(\dfrac{x^6\left(x^4-x^2+1\right)-x^3\left(x^4-x^2+1\right)+x^4-x^2+1}{x^{18}\left(x^{12}+x^6+1\right)+x^{12}+x^6+1}\)
\(Q=\dfrac{\left(x^4-x^2+1\right)\left(x^6-x^3+1\right)}{\left(x^{12}+x^6+1\right)\left(x^{18}+1\right)}\)
\(Q=\dfrac{\left(x^4-x^2+1\right)\left(x^6-x^3+1\right)}{\left(x^{12}+x^6+1\right)\left[\left(x^6\right)^3+1\right]}\)
\(Q=\dfrac{\left(x^4-x^2+1\right)\left(x^6-x^3+1\right)}{\left(x^{12}+2x^6+1-x^6\right)\left[\left(x^2\right)^3+1\right]\left(x^{12}-x^6+1\right)}\)
\(Q=\dfrac{\left(x^4-x^2+1\right)\left(x^6-x^3+1\right)}{\left[\left(x^6+1\right)-\left(x^3\right)^2\right]\left(x^2+1\right)\left(x^4-x^2+1\right)\left(x^{12}-x^6+1\right)}\)
\(Q=\dfrac{\left(x^6-x^3+1\right)}{\left(x^6-x^3+1\right)\left(x^6+1+x^3\right)\left(x^2+1\right)\left(x^{12}-x^6+1\right)}\)
\(Q=\dfrac{1}{\left(x^6+1+x^3\right)\left(x^2+1\right)\left(x^{12}-x^6+1\right)}\)
Bài 6:
a) Ta có: \(x^2-4xy+4y^2-2x+4y-35\)
\(=\left(x-2y\right)^2-2\left(x-2y\right)-35\)
\(=\left(x-2y\right)^2-7\cdot\left(x-2y\right)+5\left(x-2y\right)-35\)
\(=\left(x-2y\right)\left(x-2y-7\right)+5\left(x-2y-7\right)\)
\(=\left(x-2y-7\right)\left(x-2y+5\right)\)
b) Ta có: \(\left(x^2+x+1\right)\left(x^2+x+2\right)-12\)
\(=\left(x^2+x\right)^2+3\cdot\left(x^2+x\right)+2-12\)
\(=\left(x^2+x\right)^2+3\cdot\left(x^2+x\right)-10\)
\(=\left(x^2+x\right)^2+5\left(x^2+x\right)-2\left(x^2+x\right)-10\)
\(=\left(x^2+x\right)\left(x^2+x+5\right)-2\left(x^2+x+5\right)\)
\(=\left(x^2+x+5\right)\left(x^2+x-2\right)\)
\(=\left(x^2+x+5\right)\left(x^2+2x-x-2\right)\)
\(=\left(x^2+x+5\right)\left(x-1\right)\left(x+2\right)\)
c) Ta có: \(\left(x+2\right)\left(x+4\right)\left(x+6\right)\left(x+8\right)+16\)
\(=\left(x^2+10x+16\right)\left(x^2+10x+24\right)+16\)
\(=\left(x^2+10x\right)^2+40\left(x^2+10x\right)+384+16\)
\(=\left(x^2+10x\right)^2+40\left(x^2+10x\right)+400\)
\(=\left(x^2+10x+20\right)^2\)
d) Ta có: \(\left(x+2\right)\left(x+3\right)\left(x+4\right)\left(x+5\right)-24\)
\(=\left(x^2+7x+10\right)\left(x^2+7x+12\right)-24\)
\(=\left(x^2+7x\right)^2+22\left(x^2+7x\right)+120-24\)
\(=\left(x^2+7x\right)^2+22\left(x^2+7x\right)+96\)
\(=\left(x^2+7x\right)^2+16\left(x^2+7x\right)+6\left(x^2+7x\right)+96\)
\(=\left(x^2+7x\right)\left(x^2+7x+16\right)+6\left(x^2+7x+16\right)\)
\(=\left(x^2+7x+16\right)\left(x^2+7x+6\right)\)
\(=\left(x^2+7x+16\right)\left(x+1\right)\left(x+6\right)\)
e) Ta có: \(x\left(x+4\right)\left(x+6\right)\left(x+10\right)+128\)
\(=\left(x^2+10x\right)\left(x^2+10x+24\right)+128\)
\(=\left(x^2+10x\right)^2+24\left(x^2+10x\right)+128\)
\(=\left(x^2+10x\right)^2+16\left(x^2+10x\right)+8\left(x^2+10x\right)+128\)
\(=\left(x^2+10x\right)\left(x^2+10x+16\right)+8\left(x^2+10x+16\right)\)
\(=\left(x^2+10x+16\right)\left(x^2+10x+8\right)\)
\(=\left(x+2\right)\left(x+8\right)\left(x^2+10x+8\right)\)
a, ( x2 + x )2 - 14 ( x2 + x ) + 24
= (x2 + x)2 - 2(x2 + x) -12(x2 + x) + 24
= (x2 + x).(x2 + x -2) - 12(x2 + x -2)
= (x2 + x -2).(x2 + x -12)
= (x2 + 2x - x - 2).(x2 + 4x - 3x - 12)
=[x.(x+2)-(x+2)].[x.(x+4)-3(x+4)]
= (x+2).(x-1).(x+4).(x-3)
= x4 + 2x3 - 13x2 - 14x + 24
b, ( x2 + x )2 + 4x2 + 4x - 12
= x4 + 2x3 + x2 + 4x2 + 4x -12
= x4 + 2x3 + 5x2 + 4x -12
c, x4 + 2x3 + 5x2 + 4x - 12
= x4 - x3 + 3x3 - 3x2 + 8x2 - 8x +12x -12
= x3(x-1) + 3x2(x-1) + 8x(x-1) + 12(x-1)
= (x-1) . (x3 + 3x2 + 8x +12)
= (x-1) . ( x3 +2x2 + x2 + 2x + 6x +12)
= (x-1). [x2(x+2) + x(x+2) + 6(x+2)]
= (x-1).(x+2).(x2 + x+ 6)
a, Đặt (x2 +x ) = t ta có:
=> t2 + 4t - 12 = 0
=> ( t + 2)2 - 16 = 0
=> ( t + 2)2 - 42 = 0
=> ( t -2)( t + 6) = 0
=>\(\left[{}\begin{matrix}t-2=0\\t+6=0\end{matrix}\right.\)
Thay t = x2 + x
- x2 + x -2 = 0 => (x+2)(x-1) = 0 => \(\left[{}\begin{matrix}x=-2\\x=2\end{matrix}\right.\)
- x2 + x + 6 = 0 => (x+3)(x-2) = 0 => \(\left[{}\begin{matrix}x=-3\\x=2\end{matrix}\right.\)
1
x3-7x+6
=x3+0x2-7x +6
= x3-x2+x2-x-6x+6
=(x3-x2)+(x2-x)-(6x-6)
=x2(x-1)+x(x-1)-6(x-1)
=(x-1)(x2+x-6)
=(x-1)(x2+3x-2x-6)
=(x-1)[x(x+3)-2(x+3)]
=(x-1)(x-2)(x+3)
7) (x+2)(x+3)(x+4)(x+5)-24
=(x+2)(x+5) (x+3)(x+4)-24
=[x(x+5)+2(x+5)][x(x+4)+3(x+4)]-24
=[x2+5x+2x+10][x2+4x+3x+12]-24
=[x2+7x+10][x2+7x+12]-24
đặt a=x2+7x+10
=>x2+7x+12=a+2
=a(a+2)-24
=a2+2a-24
=a2+6a-4a-24
=(a2+6a)-(4a+24)
=a(a+6)-4(a+6)
=(a+6)(a-4)
thay a= x2+7x+10 vào ta được
(x2+7x+10+6)(x2+7x+10-4)
=(x2+7x+16)(x2+7x+6)
Tham khảo: