\((2x+3y)^3=(2x)^3+3.(2x)^2.3y+3.2x.(3y)^2+(3y)^3\)

\(=8x^3+36x^2y+54xy^2+27y^3\)

\(x^4-2x^3-2x^2-2x-3\)

\(=x^4+x^3-3x^3-3x^2+x^2+x-3x-3\)

\(=x^3(x+1)-3x^2(x+1)+x(x+1)-3(x+1)\)

\(=(x+1)(x^3-3x^2+x-3)\)

\(=(x+1)[x^2.(x-3)+(x-3)]\)

\(=(x+1)(x-3)(x^2+1)\) 

(30 . x + 40) : 2 = 1500 : 30 --> Sai

Sửa lại: \(\left(30x+40\right).2=1500:30\)

(30 . x + 40) : 2 = 1500 : 30 --> Sai

Sửa lại: \(\left(30x+40\right).2=1500:30\)

9kg

\(1500:\left(30x+40\right):2=30\)

⇔ \(750:\left(30x+40\right)=30\)

⇒ \(30x+40=750:30=25\)

⇔ \(30x=-15\)

⇔ \(x=-\dfrac{1}{2}\)

lười kẻ hình :v 

A. 261

B. 124