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222-9+11+12:2*14+14 = ? ( )

Toán Lớp 8: Tìm x: a) 3x(x+1)+5x=0 b) x mũ 2-5x=0 c) 4x mũ 2 – 1-( 2x+1 )=0 d) x mũ 2-7x+10=0

Toán Lớp 8: Tìm x:
a) 3x(x+1)+5x=0
b) x mũ 2-5x=0
c) 4x mũ 2 – 1-( 2x+1 )=0
d) x mũ 2-7x+10=0

1. Lời giải:
a)
3x(x+1)+5x=0
⇔3x^(2)+3x+5x=0
⇔3x^(2)+8x=0
⇔x(3x+8)=0
$⇔\left[\begin{matrix}x=0\\ 3x+8=0\end{matrix}\right.$
$⇔\left[\begin{matrix}x=0\\ 3x=-8\end{matrix}\right.$
$⇔\left[\begin{matrix}x=0\\ x=\dfrac{-8}{3}\end{matrix}\right.$
Vậy x=0 hoặc x=-8/3
b)
x^(2)-5x=0
⇔x(x-5)=0
$⇔\left[\begin{matrix}x=0\\ x-5=0\end{matrix}\right.$
$⇔\left[\begin{matrix}x=0\\ x=5\end{matrix}\right.$
Vậy x=0 hoặc x=5
c)
4x^(2)-1-(2x+1)=0
⇔(2x)^(2)-1-(2x+1)=0
⇔(2x-1)(2x+1)-(2x+1)=0
⇔(2x+1)(2x-1-1)=0
⇔(2x+1)(2x-2)=0
⇔2(2x+1)(x-1)=0
⇔(2x+1)(x-1)=0
$⇔\left[\begin{matrix}2x+1=0\\ x-1=0\end{matrix}\right.$
$⇔\left[\begin{matrix}2x=-1\\ x=1\end{matrix}\right.$
$⇔\left[\begin{matrix}x=\dfrac{-1}{2}\\ x=1\end{matrix}\right.$
Vậy x=-1/2 hoặc x=1
d)
x^(2)-7x+10=0
⇔x^(2)-2x-5x+10=0
⇔x(x-2)-5(x-2)=0
⇔(x-2)(x-5)=0
$⇔\left[\begin{matrix}x-2=0\\ x-5=0\end{matrix}\right.$
$⇔\left[\begin{matrix}x=2\\ x=5\end{matrix}\right.$
Vậy x=2 hoặc x=5