=2^3-3.2^2.3x+3.9x^2.2-(3x)^3

=(2-3x)^3=0

2-3x=0=>x=2/3

dung roi do 2 phan 3

\(8-36x+54x^2-27x^3=0\)

\(=2^3-3.2^2.3x+3.9x^2.2-3x^3\)

\(=2-3x^3=0\)

\(\Rightarrow2-3x=0\Rightarrow x=\frac{2}{3}\)

Bài 2: 

a: \(A=a^2+b^2+c^2+2ab-2ac-2bc+a^2+b^2+c^2-2ab-2bc+2ac\)

\(=2a^2+2b^2+2c^2-4bc\)

\(=2+2\cdot9+2\cdot1-4\cdot3\cdot\left(-1\right)=22+12=34\)

b: \(B=\left(a+b-a+b\right)\left(a+b+a-b\right)=4ab=4\cdot2\cdot5=40\)

a) 9x⁴+16y⁶-24x²y³

=(3x²)²-2.3x².4y³+(4y³)²

=(3x²-4y³)²

b) 16x²-24xy+9y²

=(4x)²-2.4x.3y+(3y)²

=(4x-3y)²

c) 36x²-(3x-2)²

=(36x-3x+2)(36x+3x-2)

=(33x+2)(39x-2)

d) 27x³+54x²y+36xy²+8y³

=(3x)³+3.(3x)².2y+3.3x.(2y)²+(2y)³

=(3x+2y)³

e) y⁹-9x²y⁶+27x⁴y³-27x⁶

=(y³)³-3.(y³)².3x²+3.y³.(3x²)²-(3x²)³

=(y³-3x²)³

f) 64x³+1

= (4x)³+1³

=(4x+1)[(4x)²-4x.1+1²]

=(4x+1)(16x²-4x+1)

e) 27x⁶-8x³  *sửa đề*

=(3x²)³-(2x)³

=(3x²-2x)[(3x)²+3x².2x+(2x)²]

=(3x²-2x)(9x²+6x³+4x²)

~~~

\(A=36x^2+24x+7\)

\(A=\left(6x\right)^2+2.6x.2+2^2+3\)

\(A=\left(6x+2\right)^2+3\)

Vì \(\left(6x+2\right)^2\ge0\forall x\)

\(\Rightarrow\left(6x+2\right)^2+3\ge3\forall x\)

\(\Rightarrow A\ge3\forall x\)

\(\Rightarrow A=3\Leftrightarrow\left(6x+2\right)^2=0\)

\(\Leftrightarrow6x+2=0\)

\(\Leftrightarrow6x=-2\)

\(\Leftrightarrow x=-\frac{1}{3}\)

Vậy  \(Amin=3\Leftrightarrow x=-\frac{1}{3}\)

36x²+24x+7

=36x²+24x+4+3

=(36x²+24x+4)+3

=(6x+2)²+3

vì bình phương của 1 số luôn lớn hơn hoặc bằng 0  

suy ra (6x+2)²>=0

suy ra (6x+2)²+3>=3

Min của A=3 khi:

6x+2=0

6x= -2

x=-2/6

vậy Mim của A=3 khi x=-2/6

B. \(2-\frac{13}{3}< x< 1-2,4\)

\(-\frac{7}{3}< x< -\frac{7}{5}\)

\(\Rightarrow x=-\frac{7}{4}\)

C. 13x + 350 = 1000

13x = 650

x = 50 

D. \(\frac{4}{7}x-\frac{5}{8}=\frac{17}{24}\)

\(\frac{4x}{7}=\frac{4}{3}\)

\(\Rightarrow12x=28\)

\(\Rightarrow x=\frac{7}{3}\)

E. \(\frac{3}{7}x=5\)

\(x=5:\frac{3}{7}=\frac{5.7}{3}=\frac{35}{3}\)

Vì \(x\in Z\Rightarrow x\in O\)

G. 10 

bn đưa ra câu hỏi thế này

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