ko ai giải đc à, giúp mk đi mà mau lên đang cần gấp, please

RẤT nhieu bn giai dc vi các pt này dễ nhung k ai giai vi nó dài ,làm mệt mà kè nhờ vả k biet ơn, k coi trọng chât xám 

toàn là h tảo lao nên ng tài k dc trọng dụng , kẻ bât tai thi k giai dc, bởi z ng tài chỉ xem bài nào khó, k dài thi giai, dc kdc h cũng k cần

\(\left(x^2+4x-5\right)\left(x^2+4x-21\right)=297\)

đặt a = \(x^2+4x-5\) vào bt ta được:

\(a\left(a-16\right)-297=0\Leftrightarrow a^2-16a+64-361=0\)

\(\Leftrightarrow\left(a-8\right)^2-19^2=0\Leftrightarrow\left(a-27\right)\left(a+11\right)=0\)

\(\Leftrightarrow\left(x^2+4x-32\right)\left(x^2+4+6\right)=0\)

\(\Leftrightarrow\left(x-4\right)\left(x+8\right)\left(\left(x+2\right)^2+2\right)=0\)

\(\left\{{}\begin{matrix}x-4=0\\x+8=0\\\left(x+2\right)^2=-2\end{matrix}\right.\Rightarrow\left\{{}\begin{matrix}x=4\\x=-8\end{matrix}\right.\)

\(\left(x-1\right)\left(x-3\right)\left(x+5\right)\left(x+7\right)=297\)

\(\Leftrightarrow\left(x^2-3x-x+3\right)\left(x^2+7x+5x+35\right)=297\)

\(\Leftrightarrow\left(x^2-4x+3\right)\left(x^2+12x+35\right)=297\)

\(\Leftrightarrow x^4+12x^3+35x^2-4x^3-48x^2-140x+3x^2+36x+105=297\)

\(\Leftrightarrow x^4+8x^3-10x^2-104x+105-297=0\)

\(\Leftrightarrow x^4-4x^3+12x^3-48x^2+38x^2-152x+48x-192=0\)

\(\Leftrightarrow x^3\left(x-4\right)+12x^2\left(x-4\right)+38x\left(x-4\right)+48\left(x-4\right)=0\)

\(\Leftrightarrow\left(x-4\right)\left(x^3+12x^2+38x+48\right)=0\)

\(\Leftrightarrow\left(x-4\right)\left(x^3+8x^2+4x^2+32x+6x+48\right)=0\)

\(\Leftrightarrow\left(x-4\right)\left[x^2\left(x+8\right)+4x\left(x+8\right)+6\left(x+8\right)\right]=0\)

\(\Leftrightarrow\left(x-4\right)\left(x+8\right)\left(x^2+4x+6\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}x-4=0\\x+8=0\\x^2+4x+6=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=4\\x=-8\\x\notin R\end{matrix}\right.\)

\(S=\left\{4;-8\right\}\)

\(\left(x-1\right)\left(x+5\right)\left(x-3\right)\left(x+7\right)-297=0\)

\(\Leftrightarrow\left(x^2+4x-5\right)\left(x^2+4x-21\right)-297=0\)

gọi \(x^2+4x-5=y\) ta có :

\(y\left(y-16\right)-297=0\)

\(\Leftrightarrow y^2-16y-297=0\)

\(\Leftrightarrow\left(y-27\right)\left(y+11\right)=0\)

\(\Leftrightarrow\left(x^2-4x-32\right)\left(x^2-4x+6\right)=0\)

\(\Leftrightarrow\left(x-8\right)\left(x+4\right)\left(x^2-4x+6\right)=0\)

\(\Rightarrow\left(x-8\right)\left(x+4\right)=0\) ( VÌ \(x^2-4x+6=\left(x-2\right)^2+2\) )

còn lại tự làm :))

a, \(\left(x^2+x\right)^2+4\left(x^2+x\right)-12=0\)

\(\Leftrightarrow x^4+2x^3+x^2+4x^2+4x+12=0\)

\(\Leftrightarrow x^4+2x^3+5x^2+4x-12=0\)

\(\Leftrightarrow x^4-x^3+3x^3-3x^2+8x^2-8x+12x-12=0\)

\(\Leftrightarrow x^3\left(x-1\right)+3x^2\left(x-1\right)+8x\left(x-1\right)+12\left(x-1\right)=0\)

\(\Leftrightarrow\left(x^3+3x^2+8x+12\right)\left(x-1\right)=0\)

\(\Leftrightarrow\left(x^3+2x^2+x^2+2x+6x+12\right)\left(x-1\right)=0\)

\(\Leftrightarrow\left[x^2\left(x+2\right)+x\left(x+2\right)+6\left(x+2\right)\right]\left(x-1\right)=0\)

\(\Leftrightarrow\left(x^2+x+6\right)\left(x+2\right)\left(x-1\right)=0\)

có : \(x^2+x+6>0\)

\(\Leftrightarrow\orbr{\begin{cases}x+2=0\\x-1=0\end{cases}\Leftrightarrow\orbr{\begin{cases}x=-2\\x=1\end{cases}}}\)

b,  \(\left(x-1\right)\left(x-3\right)\left(x+5\right)\left(x+7\right)-297=0\)

\(\Leftrightarrow\left[\left(x-1\right)\left(x+5\right)\right]\left[\left(x-3\right)\left(x+7\right)\right]-297=0\)

\(\Leftrightarrow\left(x^2+4x-5\right)\left(x^2+7x-21\right)-297=0\)

đặt \(x^2+4x-13=t\)

\(\Leftrightarrow\left(t+8\right)\left(t-8\right)-297=0\)

\(\Leftrightarrow t^2-64-297=0\)

\(\Leftrightarrow t^2=361\)

\(\Leftrightarrow t=\pm19\)

có t rồi tìm x thôi

( x - 1 ) ( x - 3 ) ( x + 5 ) ( x + 7) - 297 = 0

<=> ( x² + 4x - 5 ) ( x² + 4x - 21 ) - 297 = 0

Đặt x² + 4x - 5 = t ( t > -9 )

Ta có : t (t - 16 ) - 297 = 0 <=> t² - 16t - 297  = 0 <=>  t = 27 ; t = 11 ( loại)

Ta có x² + 4x - 5 = 27 <=> x² + 4x - 32 = 0  <=> x = 4 , x = -8

TA CÓ:

\(a,\left(4x-1\right)\left(x-3\right)=\left(x-3\right)\left(5x+2\right)\Leftrightarrow\left(4x-1\right)\left(x-3\right)-\left(x-3\right)\left(5x+2\right)=0\)

\(\left(x-3\right)\left(4x-1-5x-2\right)=0\Leftrightarrow\left(x-3\right)\left(-x-3\right)=0\orbr{\begin{cases}x=3\\x=-3\end{cases}}\)

\(b,\left(x+3\right)\left(x-5\right)+\left(x+3\right)\left(3x-4\right)=0\Leftrightarrow\left(x+3\right)\left(x-5+3x-4\right)=0\)

\(\left(x-3\right)\left(4x-9\right)=0\orbr{\begin{cases}x=3\\x=\frac{9}{4}\end{cases}}\)

\(c,\left(1-x\right)\left(5x+3\right)=\left(3x-7\right)\left(x-1\right)\Leftrightarrow\left(1-x\right)\left(5x+3\right)=\left(7-3x\right)\left(1-x\right)\)

\(\left(1-x\right)\left(5x+3-7+3x\right)=0\Leftrightarrow\left(1-x\right)\left(8x-4\right)=0\orbr{\begin{cases}x=1\\x=\frac{1}{2}\end{cases}}\)

a) \(=x^3-\dfrac{1}{27}-x^2+\dfrac{2}{3}x-\dfrac{1}{9}=x^3-x^2+\dfrac{2}{3}x-\dfrac{2}{27}\)

b) \(=x^6-6x^4+12x^2-8-x^3+x+x^2-3x=x^6-6x^4-x^3+13x^2-2x-8\)

\(=x^6-6x^4+12x^2-8-x^3+x+6x^2-18x\\ =x^6-6x^4-x^3+18x^2-17x-8\)

a: =>(x^2+4x-5)(x^2+4x-21)=297

=>(x^2+4x)^2-26(x^2+4x)+105-297=0

=>x^2+4x=32 hoặc x^2+4x=-6(loại)

=>x^2+4x-32=0

=>(x+8)(x-4)=0

=>x=4 hoặc x=-8

b: =>(x^2-x-3)(x^2+x-4)=0

hay \(x\in\left\{\dfrac{1+\sqrt{13}}{2};\dfrac{1-\sqrt{13}}{2};\dfrac{-1+\sqrt{17}}{2};\dfrac{-1-\sqrt{17}}{2}\right\}\)

c: =>(x-1)(x+2)(x^2-6x-2)=0

hay \(x\in\left\{1;-2;3+\sqrt{11};3-\sqrt{11}\right\}\)