Question

6)  tìm x biết  4x-1-x(2x+1)=0

7)  tìm n thuộc X để 6n^2+n-1 chia hết cho 3n+2.

Answer 1

4x-1-x(2x+1)=0

<=>4x-1-2x²-x=0

<=>-2x²+3x-1=0

<=>-2x²+2x+x-1=0

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

<=>(x-1)(1-2x)=0

<=>x-1=0 hoặc 1-2x=0

<=>x=1 hoặc x=1/2

Answer 2

\(\frac{6n^2+n-1}{3n+2}=\frac{6n^2+4n}{3n+2}-\frac{3n+2}{3n+2}+\frac{1}{3n+2}=2n-1+\frac{1}{3n+2}\)

6n²+n-1 chia hết cho 3n+2 <=>1 chia hết cho 3n+1

<=>3n+2 là Ư(1)={+-1}

*)3n+2=1<=>x=-1/3(L)

*)3n+2=-1<=>x=-1

Vậy x=-1