Question

bài 1: rút gọn biểu thức 

a, (3x+4y).(9\(x^2\) - 12y+16\(y^2\)) 

b,\(\left(x+3\right)^3\) - \(\left(3x-1\right)^2\)

 

 

Answer 1

a: \(\left(3x+4y\right)\left(9x^2-12y+16y^2\right)\)

\(=27x^3-36xy+48xy^2+36x^2y-48y^2+64y^3\)

b: \(\left(x+3\right)^3-\left(3x-1\right)^2\)

\(=x^3+9x^2+27x+27-\left(9x^2-6x+1\right)\)

\(=x^3+9x^2+27x+27-9x^2+6x-1\)

\(=x^3+33x+26\)

Answer 2

`#3107.101107`

`1.`

`a,`

`(3x + 4y)(9x^2 - 12xy + 16y^2)?`

`= (3x)^3 + (4y)^3`

`= 27x^3 + 64y^3`

`b,`

`(x + 3)^3 - (3x - 1)^2`

`= x^3 + 9x^2 + 27x + 27 - (9x^2 - 6x + 1)`

`= x^3 + 9x^2 + 27x + 27 - 9x^2 + 6x - 1`

`= x^3 + 33x + 26`

_____

Sử dụng HĐT:

`A^3 + B^3 = (A + B)(A^2 + AB + B^2)`

`(A + B)^3 = A^3 + 3A^2B + 3AB^2 + B^3`

`(A - B)^2 = A^2 - 2AB + B^2.`