a) \(x^3+6x^2+12x+8\)
\(=\left(x+2\right)^3\)
b) \(x^3-3x^2+3x-1\)
\(=\left(x-1\right)^3\)
c) \(1-9x+27x^2-27x^3\)
\(=-\left(27x^3-27x^2+9x-1\right)\)
\(=-\left(3x-1\right)^3\)
d) \(x^3+\frac{3}{2}x^2+\frac{3}{4}x+\frac{1}{8}\)
\(=\left(x+\frac{1}{2}\right)^3\)
e) \(27x^3-54x^2y+36xy^2-8y^3\)
\(=\left(3x-2y\right)^3\)
a) x^3+6x^2+12x+8
=(x+2)^3
b)x^3-3x^2+3x-1
=(x-1)^3
c)1-9x+27x^2-27x^3
=(1-3x)^3
d)x^3+3/2x^2+3/4x+1/8
=(x+1/2)^3
e)27x^3-54x^2y+36xy^2-8y^3
=(3x-2y)^3
Chúc cậu học tốt!and......mình làm hơi tắt cậu làm đầy đủ nha!Cảm ơn!
x3 + 6x2 + 12x + 8 = x3 + 3.x2.2 + 3.x.22 + 23 = ( x + 2 )3
x3 - 3x2 + 3x - 1 = ( x - 1 )3
1 - 9x + 27x2 - 27x3 = 13 - 3.12.3x + 3.1.(3x)2 - ( 3x )3 = ( 1 - 3x )3
x3 + 3/2x2 + 3/4x + 1/8 = x3 + 3.x2.1/2 + 3.x.(1/2)2 + ( 1/2 )3 = ( x + 1/2 )3
27x3 - 54x2y + 36xy2 - 8y3 = ( 3x )3 - 3.(3x)2.2y + 3.3x.(2y)2 - ( 2y )3 = ( 3x - 2y )3
Bài làm :
\(a\text{)}x^3+6x^2+12x+8\)
\(=\left(x+2\right)^3\)
\(b\text{)}x^3-3x^2+3x-1\)
\(=\left(x-1\right)^3\)
\(c\text{)}1-9x+27x^2-27x^3\)
\(=\left(1-3x\right)^3\)
\(d\text{)}x^3+\frac{3}{2}x^2+\frac{3}{4}x+\frac{1}{8}\)
\(=\left(x+\frac{1}{2}\right)^3\)
\(e\text{)}27x^3-54x^2y+36xy^2-8y^3\)
\(=\left(3x-2y\right)^3\)
Lưu ý : Các hằng đẳng thức sử dụng :
(a+b)3 = (a3 + 3a2b + 3ab2 + b3) (a-b)3 = (a3 - 3a2b + 3ab2 - b3)
