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
