(x+1)(x-4)(x+2)(x-8)+4x^2

=[(x+1)(x-8)][(x-4)(x+2)]+4x²

=(x²-7x-8)(x²-2x-8)+4x²

Đặt t=x²-2x-8 ta được:

(t-5x).t+4x²

=t²-5xt+4x²

=t²-xt-4xt+4x²

=t.(t-x)-4x.(t-x)

=(t-x)(t-4x)

thay t=x²-2x-8 ta được:

(x²-3x-8)(x²-6x-8)

Vậy (x+1)(x-4)(x+2)(x-8)+4x^2=(x²-3x-8)(x²-6x-8)

fan son tung

Ta có:

\(\left(x-1\right)\left(x+2\right)\left(x+3\right)\left(x-6\right)+32x^2\)

\(=\left(x^2-7x+6\right)\left(x^2+5x+6\right)+32x^2\)

Đặt : \(x^2+6=a\left(a< 0\right)\). Khi đó pt trở thành:

\(\left(a-7x\right)\left(a+5x\right)+32x^2\)

\(=a^2-2ax-3x^2=\left(a+x\right)\left(a-3x\right)\)

\(=\left(x^2+x+6\right)\left(x^2-3x+6\right)\)

a)x⁷+x⁵+1=x⁷+x⁶-x⁶+2x⁵-x⁵+x⁴-x⁴+x³-x³+x²-x²+1

=x⁷-x⁶+x⁵-x³+x²+x⁶-x⁵+x⁴-x²+x+x⁵-x⁴+x³-x+1

=x²(x⁵-x⁴+x³-x+1)+x(x⁵-x⁴+x³-x+1)+1(x⁵-x⁴+x³-x+1)

=(x²+x+1)(x⁵-x⁴+x³-x+1)

b)4x⁴-32x²+1=4x⁴+12x³+2x²-12x³-36x²-6x+2x²+6x+1

=2x²(2x²+6x+1)-6x(2x²+6x+1)+1(2x²+6x+1)

=(2x²-6x+1)(2x²+6x+1)

c)x⁶+27=(x²+3)(x²-3x+3)(x²+3x+3)

d)3(x⁴+x²+1)-(x²+x+1)

=3x⁴-3x³+2x²+3x³-3x²+2x+3x²-3x+2

=x²(3x²-3x+2)+x(3x²-3x+2)+1(3x²-3x+2)

=(x²+x+1)(3x²-3x+2)

e)bạn tự làm nhé

1.  (x-1)(x-3)(x-5)(x-7)-20=0
<=> (x-1)(x-7)(x-3)(x-5)-20=0
<=> (x^2-8x+7)(x^2-8x+15)-20=0
Đặt x^2-8x+7=a => x^2-8x+15= a+8
=> a(a+8)-20=0
<=> a^2+8a-20=0
<=>(a^2+8a+16)-36=0
<=> (a+4)^2=36
=> {a+4=6a+4=−6{a+4=6a+4=−6
<=>{a=2a=−10{a=2a=−10
*a=2 => x^2-8x+7=2
<=> x^2-8x+5=0
<=>(x^2-8x+16)-11=0
<=>(x-4)^2=11
<=>x-4=√11
<=> x=√11 +4
*a=-10 => x^2-8x+7=-10
<=> x^2-8x+17=0
<=> (x^2-8x+16)+1=0
<=> (x-4)^2=-1 (PT vô nghiệm)
Vậy pt có nghiệm x=√11 +4

mk chỉ biết vậy thôi

3, \(x\left(x-1\right)\left(x+1\right)\left(x+2\right)-3=\left(x^2+x\right)\left(x^2+x-2\right)-3\)

Đặt \(x^2+x=t\)

\(t\left(t-2\right)-3=t^2-2t-3=\left(t-3\right)\left(t+1\right)\)

Theo cách đặt \(\left(x^2+x-3\right)\left(x^2+x+1\right)\)

1, \(\left(x-1\right)\left(x-3\right)\left(x-5\right)\left(x-7\right)-20\)

\(=\left(x^2-8x+7\right)\left(x^2-8x+15\right)-20\)

Đặt  \(x^2-8x+7=t\)

\(t\left(t+8\right)-20=t^2+8t-20=\left(t-2\right)\left(t+10\right)\)

Theo cách đặt \(\left(x^2-8x+5\right)\left(x^2-8x+17\right)\)

ta có

\(5x=-3y=4z\)

\(\Rightarrow\frac{x}{12}=-\frac{y}{20}=\frac{z}{15}\)

\(\Rightarrow\frac{x}{12}=-\frac{y}{20}=\frac{3z}{45}=\frac{x-y+3z}{12+20+45}=\frac{7}{77}=\frac{1}{11}\)

\(\Rightarrow\hept{\begin{cases}x=\frac{1}{11}.12=\frac{12}{11}\\-y=\frac{1}{11}.20=\frac{20}{11}\\3z=\frac{1}{11}.45=\frac{45}{11}\end{cases}}\)

\(\Rightarrow\hept{\begin{cases}x=\frac{12}{11}\\y=-\frac{20}{11}\\z=\frac{45}{11}:3=\frac{15}{11}\end{cases}}\)

Vậy \(\hept{\begin{cases}x=\frac{12}{11}\\y=\frac{-20}{11}\\z=\frac{15}{11}\end{cases}}\)