Question

Tìm x:

a) (3x+4)(4-x)=0

b) 3x(x-4)-2(x-4)=0

c) 7x²-28=0

Answer 1

a) \(\left(3x+4\right)\left(4-x\right)=0\Rightarrow\orbr{\begin{cases}3x+4=0\\4-x=0\end{cases}}\)

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

\(\Rightarrow x=\left\{\frac{-4}{3};4\right\}\)

b) \(\Rightarrow\orbr{\begin{cases}3\left(x-4\right)=0\\2\left(x-4\right)=0\end{cases}}\)

\(\Rightarrow\orbr{\begin{cases}x-4=0\\x-4=0\end{cases}}\Rightarrow x=4\)

c) => 7x²=0+28

=> x²=28:7

=> x²=4

=> x²=2²= (-2)²

=> x={-2;2}