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

0 bình luận về “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”

1. 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

    

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