Tìm x, biết: a) 9x^2-25=0 b) (x+1)^2-(x-4)(x+4)=8 c) (3x-1)^2+(x+3)^2-10(x+1)(x-1)=0 d) (x+3)^3+(2x+1)(4x^2-2x+1)-9x^2(x+1)=54 e) (x-3)^3-(x-3)(x^2+3x+9)+9(x+1)^2=-33

a) 9x² - 25 = 0

⇔ 9x² = 25

⇔ x² = 25 : 9

⇔ x = $\frac{5}{3}$ 

⇔ x = -$\frac{5}{3}$

b) (x+1)²-(x-4)(x+4)=8

⇔ x² + 2x + 1 - (x²-16) = 8

⇔ x² + 2x + 1 - x² + 16 = 8

⇔· 2x + 17 = 8

⇔ 2x = 8 - 17

⇔ 2x = -9

⇔ x =-$\frac{9}{2}$ 

c) (3x-1)²+(x+3)²-10(x+1)(x-1)

⇔ 9x²-6x+1+x²+6x+9-10(x²-1)

⇔ 9x² + 1 + x² + 9 - 10x² + 10

= 0

⇔ 0 + 20

= 0

⇔ 20

= 0 ( pt vô nghiệm )

d) (x+3)³+(2x+1)(4x²-2x+1)-9x²(x+1)=54

⇔ x³+9x²+27x+27+8x³+1-9x³-9x²=54

⇔ 0 + 27x + 28 + 54

⇔ 27x = 54 - 28

⇔ 27x = 26

⇔ x =n$\frac{26}{27}$ 

e) (x-3)³-(x-3)(x²+3x+9)+9(x-1)²=-33

⇔ x³-9x²+27x-27-(x³-27)+9(x²-2x+1)=-33

⇔ x³ - 9x² + 27x - 27² - x³ + 27 + 9x² - 18x + 9 = -33

⇔ 9x + 9 = -33

⇔ 9x = -33-9

⇔ 9x = -42

⇔ x = -$\frac{14}{3}$ 

@giahanchau