Môn Toán Lớp 8: Mình cần gấp 3 câu này: 1. -x ² – 2x – 1= 0 2. 4(2x-1) ² – 25(2-3x) ² = 0 3. 9(x-2) ² – 1/36(1-3x) ² = 0

Giải đáp:

1)

-x^2-2x-1=0

=>-(x^2+2x+1)=0

=>-(x+1)^2=0

=>x+1=0

=>x=-1

Vậy x=-1

2)

4(2x-1)^2-25(2-3x)^2=0

=>[2(2x-1)]^2-[5(2-3x)]^2=0

=>[4x-2]^2-[10-15x]^2=0

=>[4x-2-10+15x][4x-2+10-15x]=0

=>[19x-12][8-11x]=0

=> \(\left[ \begin{array}{l}19x-12=0\\8-11x=0\end{array} \right.\) => \(\left[ \begin{array}{l}x=\dfrac{12}{19}\\x=\dfrac{8}{11}\end{array} \right.\) 

Vậy x\in{8/11;12/19}

3)

9(x-2)^2-1/36(1-3x)^2=0

=>[3(x-2)]^2-[1/6(1-3x)]^2=0

=>[3x-6]^2-[1/6-1/2x]^2=0

=>[3x-6-1/6+1/2x][3x-6+1/6-1/2x]=0

=>[7/2x-37/6][5/2x-35/6]=0

=> \(\left[ \begin{array}{l}\dfrac{7}{2}x-\dfrac{37}{6}=0\\\dfrac{5}{2}x-\dfrac{35}{6}=0\end{array} \right.\) => \(\left[ \begin{array}{l}x=\dfrac{37}{21}\\x=\dfrac{7}{3}\end{array} \right.\) 

Vậy x\in{7/3;37/21}