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) Sửa đề: \(8x^3+36x^2+54x+27\)

Ta có: \(8x^3+36x^2+54x+27\)

\(=\left(2x\right)^3+3\cdot\left(2x\right)^2\cdot3+3\cdot2x\cdot3^2+3^3\)

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

b) Ta có: \(x^2+4x+4\)

\(=x^2+2\cdot x\cdot2+2^2\)

\(=\left(x+2\right)^2\)

=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

a, x²-x+1/4=(x-1/2)²

b, (x+1)³

c,(2x+1)³

d, (2-3x0³

e, (10x)²-(x²+25)²=:[10x+(x²+25)][10x-(x²+25)]=(10x+x²+25)(10x-x²-25)

Tại x = 103/2 ta có :

\(M=5.\left(\dfrac{103}{2}\right)^3-36.\left(\dfrac{103}{2}\right)^2+54.\dfrac{103}{2}+27=590281,375\)

a. \(7x-x^2-6=0\)

\(\Rightarrow-x^2+7x-6=0\)

\(\Rightarrow-x^2+x+6x-6=0\)

\(\Rightarrow-x\left(x-1\right)+6\left(x-1\right)=0\)

\(\Rightarrow\left(x-1\right)\left(-x+6\right)=0\)

+) Nếu \(x-1=0\Rightarrow x=1\)

+) Nếu \(-x+6=0\Rightarrow x=6\)

Vậy x=1 hoặc x=6

b. \(8x^3-36x^2+57x-27=0\)

\(\Rightarrow\left(2x\right)^2-3.2^2.x^2.3+3.2x.3^2-3^3=0\)

\(\Rightarrow\left(2x-3\right)^3=0\)

\(\Rightarrow2x-3=0\Rightarrow x=\frac{3}{2}\)

Vậy...........

Bài 1: 

b: \(=\left(x^2+x+4\right)^2+3x\left(x^2+x+4\right)+5x\left(x^2+x+4\right)+15x^2\)

\(=\left(x^2+x+4+3x\right)\left(x^2+x+4+5x\right)\)

\(=\left(x^2+4x+4\right)\left(x^2+6x+4\right)\)

\(=\left(x+2\right)^2\cdot\left(x^2+6x+4\right)\)

c: \(=25x^2-49y^2-\left(5x+7y\right)\)

\(=\left(5x-7y\right)\left(5x+7y\right)-\left(5x+7y\right)\)

\(=\left(5x+7y\right)\left(5x-7y-1\right)\)

d: \(8x^3-36x^2+54x-27=\left(2x-3\right)^3\)

bn viết từng câu đi mik giải cho

a ) \(\left(x+2\right)^3-\left(x-2\right)^3\)

    \(=\left[\left(x+2\right)-\left(x-2\right)\right]\left[\left(x+2\right)^2+\left(x+2\right)\left(x-2\right)+\left(x-2\right)^2\right]\)