Toán 8 ... Help :)

E

eye_smile

c,${x^3}=4x$
\Leftrightarrow $x(x-2)(x+2)=0$


d,${x^2}-9x+8=0$
\Leftrightarrow $(x-8)(-1)=0$


e, ${x^2}+5x+6=0$
\Leftrightarrow $(x+2)(x+3)=0$
 
K

kenhaui

e, $x^2$ + $5x$ + $6$ = 0
\Leftrightarrow$x^2$ + $2x$ +$3x$ +$6$ = 0
\Leftrightarrow$x$($x$ +$2$) +$3$($x$ +$2$) = 0
\Leftrightarrow($x$ + $2$ )($x$ +$3$ ) = 0
\Rightarrow$x$ +$2$ = 0 hoặc $x$ +$3$ = 0
\Rightarrow $x$= $ -2$ hoặc $x$ = $ - 3$
 
N

nhuquynhdat

a) $\dfrac{x+29}{31}- \dfrac{x+27}{33}= \dfrac{x+17}{43} - \dfrac{x+15}{45}$

$\leftrightarrow \dfrac{x+29}{31}+1- \dfrac{x+27}{33}-1= \dfrac{x+17}{43}+1 - \dfrac{x+15}{45}-1$

$\leftrightarrow \dfrac{x+60}{31}- \dfrac{x+60}{33}= \dfrac{x+60}{43}- \dfrac{x+60}{45}$

$\leftrightarrow (x+60)(\dfrac{1}{31}- \dfrac{1}{33}- \dfrac{1}{43}+ \dfrac{1}{45})=0$

$\leftrightarrow x+60=0 \leftrightarrow x=-60$
 
B

baochauhn1999

Câu a:
$\frac{x+29}{31} - \frac{x+27}{33}=\frac{x+17}{43} - \frac{x+15}{45}$
$<=>(\frac{x+29}{31} + 1) - (\frac{x+27}{33} + 1) = (\frac{x+17}{43} + 1) - (\frac{x+15}{45} + 1)$
$<=>\frac{x+60}{31} - \frac{x+60}{33} = \frac{x+60}{43} - \frac{x+60}{45}$
$<=>(x+60)(\frac{1}{31} + \frac{1}{45} - \frac{1}{33} - \frac{1}{43})=0$
$<=>x+60=0$
$<=>x=-60$
 
K

kenhaui

d, $x^2$ -$9x$ + $8$ = $0$
\Leftrightarrow$x^2$ $-x$ $-8x$ + $8$ =0
\Leftrightarrow$x$($x$ $-1$) $-8$($x$ $-1$) = 0
\Leftrightarrow($x$ $-8$ )($x$ $-1$) = 0
\Rightarrow$x$ $-8$ = $0$ $hoặc$ $x$ $-1$ = 0
\Rightarrow$x$ = $8$ $hoặc$ $x$ = $1$

 
B

baochauhn1999

Câu f:
$\frac{3}{x+1}+\frac{2}{x+2}=\frac{5x+4}{x^2+3x+2}$
$<=>\frac{3(x+2)}{(x+1)(x+2)}+\frac{2(x+1)}{(x+2)(x+1)}-\frac{5x+4}{(x+1)(x+2)}=0$
$<=>\frac{4}{(x+1)(x+2)}=0$
$=>PT$ vô nghiệm
 
K

kenhaui

c, $x^3$ = $4x$
\Leftrightarrow$x^3$ $-4x$ = 0
\Leftrightarrow$x$($x^2$ $-4$) = 0
\Leftrightarrow$x$($x$ $-2$)($x$ + $2$ ) = 0
Đến đây dễ rồi
 
H

hiendang241

f/

ta có:$\frac{3}{x+1}$+$\frac{2}{x+2}$=$\frac{5x+4}{x^2+3x+2}$
\Leftrightarrow$\frac{3x+6+2x+2}{(x+1)(x+2)}$=$\frac{5x+4}{(x+2)(x+1)}$
\Leftrightarrow$\frac{5x+8}{(x-1)(x-2)}=$\frac{5x+4}{(x+1)(x+2)}
\Leftrightarrow 5x+8=5x+4
\Rightarrow phương trình vô No
 
You must log in or register to reply here.
Top Bottom