Question

1. Tìm x,biết

a,x^2-2x-3=0

b,2x^2+3=-5x

c,2(x-3)(x+1)=(2x+1)(x-3)-12

d,(2x-1)^2+(2-x)(2x-1)=0

e,-x^2+5x=6

g,(x+3)^2>6x+13

h,(x-3)^2<x^2-5x+1

Please,help me !

Answer 1

Câu a :

\(x^2-2x-3=0\)

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

\(\Leftrightarrow x\left(x-1\right)+3\left(x-1\right)=0\)

\(\Leftrightarrow\left(x-1\right)\left(x+3\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}x-1=0\Rightarrow x=1\\x+3=0\Rightarrow x=-3\end{matrix}\right.\)

Câu b :

\(2x^2+3=-5x\)

\(\Leftrightarrow2x^2+3+5x=0\)

\(\Leftrightarrow2x^2+2x+3x+3=0\)

\(\Leftrightarrow2x\left(x+1\right)+3\left(x+1\right)=0\)

\(\Leftrightarrow\left(x+1\right)\left(2x+3\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}x+1=0\Rightarrow x=-1\\2x+3=0\Rightarrow x=-\dfrac{3}{2}\end{matrix}\right.\)

Mấy câu sau khó quá ko bt làm :)