Question

Tìm x

a/ x²-20-x=0

b/ (2x+3)²-(4x²-9)=0

c/ (2x²+5x+3):(x+1)=4x-5

Answer 1

a)x²-20-x=0

<=>(x²-5x)+(4x-20)=0

<=>x(x-5)+4(x-5)=0

<=>(x-5)(x+4)=0

<=>x-5=0 hoặc x+4=0

<=>x=5 hoặc x=-4

b)(2x+3)²-(4x²-9)=0

<=>(2x+3)(2x+3)-(2x-3)(2x+3)=0

<=>(2x+3)(2x+3-2x+3)=0

<=>(2x+3).6=0

<=>2x+3=0

<=>2x=-3

<=>x=-1,5

c)(2x²+5x+3):(x+1)=4x-5

<=>2x²+5x+3=(4x-5)(x+1)

<=>2x²+5x+3=4x²-x-5

<=>4x²-x-5-2x²-5x-3=0

<=>2x²-6x-8=0

<=>x²-3x-4=0

<=>(x²-4x)+(x-4)=0

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

<=>(x-4)(x+1)=0

<=>x+1=0 hoặc x-4=0

<=>x=-1 hoặc x=4