Tìm x a. 5x ( x – 3 ) – 2x + 6 = 0 b. ( x + 2 )^2 – ( x – 2 ) ( x + 2 ) = 0 c. x^3 – 8 = ( x – 2 )^2 d. x^3 + 5x^2 – 4x – 20 = 0

a)5x ( x – 3 ) – 2x + 6 = 0

5x(x-3)-2(x-3)=0

(5x-2)(x-3)=0

=>5x-2=0=>x=2/5

hoặc x-3=0=>x=3

b)( x + 2 )^2 – ( x – 2 ) ( x + 2 ) = 0

(x+2)(x+2-x+2)=0

=>x+2=0=>x=-2

c)x^3 – 8 = ( x – 2 )^2

x³-2³=(x-2)²

(x-2)(x²+2x+4)-(x-2)²=0

(x-2)(x²+2x+4-x+2)=0

=>x-2=0=>x=2

hoặc x²-x+6=0

=>x²-2×1/2+1/4+23/4=0

=>(x-1/2)²=-23/4

=> ko tìm đc x

=> x=2

d)x^3 + 5x^2 – 4x – 20 = 0

x².x+5x²-4x-4.5=0

x²(x+5)-4(x+5)=0

(x²-4)(x+5)=0

=>x²-4=0=>x=-2,2

hoặc x+5=0=>x=-5