Question

1) Tìm x: 2x²+5x-3=0

2) tính nhanh: 3(x-3)(x+7)+(x-4)²+48 tại x=0,5

Answer 1

1) \(2x^2+5x-3=0\)

\(\Leftrightarrow2x^2+6x-x-3=0\)

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

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

\(\Rightarrow\orbr{\begin{cases}x+3=0\\2x-1=0\end{cases}\Rightarrow\orbr{\begin{cases}x=-3\\x=\frac{1}{2}\end{cases}}}\)

Answer 2

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

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

\(\Leftrightarrow\left(x-\frac{1}{2}\right)\left(x+3\right)=0\)

\(\Leftrightarrow\orbr{\begin{cases}x=\frac{1}{2}\\x=-3\end{cases}}\)

Answer 3

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

\(\Leftrightarrow2x^2+6x-x-3=0\)

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

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

\(\orbr{\begin{cases}x=\frac{1}{2}\\x=-3\end{cases}}\)