Question

giải phương trình:

a)x³-9x²+27x=19

b)(2x²+3x-z)²-5(2x²+3x+3)+24=0

c)x³-7x-6=0

Answer 1

a/. x³ - 9x² +27x - 19 = 0

<=> (x³ - 3.x² .3 + 3.3² .x - 3³) + 8 = 0

<=> (x - 3)³ + 8 = 0

<=> (x - 3 + 2) [(x - 3)² - 2(x-3) +4] = 0

<=> (x -1)(x² - 6x+ 9 -2x +6 +4) =0

<=> (x - 1)(x²  - 8x + 19) = 0

<=> x - 1 = 0 => x = 1

Vậy S = {1}

Xem lại đề câu b nha bạn?

c/. x³ + 1 -7x -7 =0 

<=> (x³ + 1) -7(x+1)=0

<=> (x+1)(x²-x+1) -7(x+1)=0

<=> (x+1)(x²-x+1-7)=0

<=> x + 1 = 0 hay x² -x - 6 = 0

<=> x = -1 hay (x² - 3x) + (2x - 6) = 0 

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

<=>                 (x - 3)(x+2) = 0

<=> x = -1 hay x = 3 hay x = -2

Vậy S = {-1;3;-2}

Answer 2

X^{3 -} X²-8X²+8X+19X-19=0

<=>X²(X-1)-8X(X-1)+19(X-1)=0

<=>(X-1)(X²-8X+19)=0

vi X^2-8X+19=(X-4)²+3>3

 

 

Answer 3

a, x³-x²- 8x² +8x+19x-19=0
<=> (x-1)(x²- 8x+19)=0
<=> x-1=0 <=> x=1
 

Answer 4

c, x³+2x²- 2x²- 4x- 3x- 6=0
(x+2)(x²-2x-3)=0
(x+2)(x²- 3x +x-3)=0
(x+2)(x-3)(x+1)=0
x=- 2
x=-1
x=3
 

Answer 5

b)(2x²+3x-1)²-5(2x²+3x+3)+24=0

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