Question

Answer 1

a: 9x+21=7x-15

=>2x=-36

hay x=-18

b: \(\Leftrightarrow5x\left(x+7\right)-\left(x+7\right)^2=0\)

=>(x+7)(5x-x-7)=0

=>(x+7)(4x-7)=0

=>x=7/4 hoặc x=-7

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

\(\Leftrightarrow x^2+3x+x^2-x-2=2x^2+2x\)

=>2x-2=2x

=>-2=0(vô lý)

Answer 2

cứu với, giải giúp em với

Answer 3

a) 7x-15=9x+21

<=>7x-9x=21+15

<=>-2x=36

<=>x=-18

Answer 4

Answer 5

5x(x+7)=x^2+14x+49

<=> 5x(x+7)=(x+7)^2

<=>5x(x+7)-(x+7)^2=0

<=>(x+7)(5x-x-7)=0

<=>(x+7)(4x-7)=0<=>x+7=0 hoặc 4x-7=0

<=>x=-7 hoặc x=7/4