Question

[ngthanhtam :))]

gấp ạaa

Answer 1

[subjects]

\(a.\left(5x-4\right)\left(4x+^{}6\right)=0\)

\(\left[\begin{array}{l}5x-4=0\Rightarrow x=\frac45\\ 4x+6=0\Rightarrow x=-\frac32\end{array}\right.\)

vậy x = \(\frac45\) hoặc \(x=-\frac32\)

\(b.3x^2+6x=x+2\)

\(3x\cdot\left(x+2\right)=x+2\)

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

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

\(\left[\begin{array}{l}3x-1=0\Rightarrow x=\frac13\\ x+2=0\Rightarrow x=-2\end{array}\right.\)

vậy x \(=\frac13\) hoặc x=-2

\(c.x^2\left(2x+1\right)+4x+2=0\)

\(x^2\left(2x+1\right)+2\cdot\left(2x+1\right)=0\)

\(\left(2x+1\right)\left(x^2+2\right)=0\)

\(\left[\begin{array}{l}2x+1=0\Rightarrow x=-\frac12\\ x^2+2=0\Rightarrow x\notin O\end{array}\right.\)

vậy \(x=-\frac12\)

\(d.x^3-5x^2-4x+20=0\)

\(x^2\cdot\left(x-5\right)-4\cdot\left(x-5\right)=0\)

\(\left(x^2-4\right)\left(x-5\right)=0\)

\(\left(x-2\right)\left(x+2\right)\left(x-5\right)=0\)

\(\left[\begin{array}{l}x-2=0\Rightarrow x=2\\ x+2=0\Rightarrow x=-2\\ x-5=0\Rightarrow x=5\end{array}\right.\)

vậy x = 2 hoặc x = -2 hoặc x = 5

\(e.\left(2x+5\right)^2=16=4^2=\left(-4\right)^2\)

\(\left[\begin{array}{l}2x+5=4\Rightarrow x=-\frac12\\ 2x+5=-4\Rightarrow x=-\frac92\end{array}\right.\)

vậy \(x=-\frac12\) hoặc \(x=-\frac92\)