=a^3+b^3+3a^2b+3ab^2-a^3+3a^2b-3ab^2+b^3-2b^3

=6a^2b

\(\left(a+b\right)^3-\left(a-b\right)^3-2b^3\\ =a^3+3a^2b+3ab^2+b^3-\left(a^3-3a^2b+3ab^2-b^3\right)-2b^3\\ =a^3+3a^2b+3ab^2+b^3-a^3+3a^2b-3ab^2+b^3-2b^3\\ =6a^2b\)

ừ chie cần k vaod chữ đúng thôi

a,Đặt a+b-c=x, c+a-b=y, b+c-a=z

=>x+y+z=a+b-c+c+a-b+b+c-a=a+b+c

Ta có hằng đẳng thức:

(x+y+z)^3-3x-3y-3z=3(x+y)(x+z)(y+z)

=>(a+b+c)^3-(b+c-a)^3-(a+c-b)^3-(a+b-c)^3=(x+y+z)^3-x^3-y^3-z^3

=3(x+y)(x+z)(y+z)

=3(a+b-c+c+a-b)(c+a-b+b+c-a)(b+c-a+a+b-c)

=3.2a.2b.2c

=24abc

mình mới có tài khoản,vậy k cho bn chỉ cần k đúng thôi đk ^^? 

chịu

\(A=\sqrt{64a^2}\cdot2a=\sqrt{\left(8a\right)^2}\cdot2a=\left|8a\right|\cdot2a\)

Với a < 0 A = 8a.(-2a) = -16a²

Với a ≥ 0 A = 8a.2a = 16a²

\(B=3\sqrt{9a^6}-6a^3=3\sqrt{\left(3a^3\right)^2}-6a^3=9\left|a^3\right|-6a^3\)

\(a,\left(a+b\right)^3-\left(a-b\right)^3-6a^2b\)

\(=a^3+3a^2b+3ab^2+b^3-a^3+3a^2b-3ab^2+b^3-6a^2b\)

\(=2b^3\)

\(b,\left(a+b\right)^3+\left(a-b\right)^3-6ab^2\)

\(=a^3+3a^2b+3ab^2+b^3+a^3-3a^2b+3ab^2-b^3-6ab^2\)

\(=2a^3\)

ai lam nhanh nhat thi minh k cho

`Answer:`

`a)`

`A=5(x+1)^2-3(x-3)^2-4(x^2-4)`

`=>A=5(x^2+2x+1)-3(x^2-6x+9)-4x^2+16`

`=>A=5x^2+10x+5-3x^2+18x-27-4x^2+16`

`=>A=(5x^2-3x^2-4x^2)+(10x+18x)+(5-27+16)`

`=>A=-2x^2+28x-6`

`b)`

`B=5(x+1)^2-3(x-3)^2-4(x+2)(x-2)`

`=2x(3x+5)-3(3x+5)-2x(x^2-4x+4)-[(2x)^2-3^2]`

`=6x^2+10x-9x-15-2x^3+8x^2-8x-4x^2+9`

`=(6x^2-4x^2+8x^2)-2x^3+(10x-9x-8x)+(-15+9)`

Thay `x=-7` vào ta được:

`B=10(-7)^2-2(-7)^3-7(-7)-6`

`=>B=10.49-2(-343)+49-6`

`=>B=490+686+49-6`

`=>B=1219`

a) \(A=1+3+3^2+...+3^{100}\)

\(3A=3+3^2+3^3+...+3^{101}\)

\(3A-A=\left(3+3^2+3^3+...+3^{101}\right)-\left(1+3+3^2+...+3^{100}\right)\)

\(2A=3^{101}-1\)

\(A=\frac{3^{101}-1}{2}\)

b) \(B=2^{100}-2^{99}+2^{98}-2^{97}+...-2^3+2^2-2+1\)

\(2B=2^{101}-2^{100}+2^{99}-2^{98}+...-2^4+2^3-2^2+2\)

\(B+2B=\left(2^{100}-2^{99}+...-2+1\right)+\left(2^{101}-2^{100}+...-2^2+2\right)\)

\(3B=2^{101}+1\)

\(B=\frac{2^{101}+1}{3}\)

a,M=2^0-2^1+2^2-2^3+2^4-2^5+.....+2^2012

2M=2^1-2^2+2^3-2^4+2^5-2^5+......-2^2012+2^2013

3M=2^0+2^2013

M=(2^0+2^2013)÷3

Vậy.......

b,N=3-3^2+3^3-3^4+3^5-3^6+.....+3^2011-3^2012

3N=3^2-3^3+3^4-3^5+3^6-3^7+......+3^2012-3^2013

4N=3-3^2013

N=(3-3^2013)÷4

Vậy........

K tao nhé ko lên lớp tao đánh m😈😈😈

Bt dễ thế mà ko làm dc😂😂😂😂😂

phần c đâu

Rút gọn biểu thức: (a+b)\(^3\) – (a–b)\(^3\)

Ta có: \(\left(a+b\right)^3-\left(a-b\right)^3\)

= \(a^3+3a^2b+3ab^2+b^3-a^3-3a^2b+3ab^2-b^3\)

= \(6ab^2\)

(a+b)³-(a-b)³ = a³+3a²b+3ab²+b³-a³+3a²b-3ab²+b³

=6a²b+2b³ =2b(3a² +b²)