Câu 5: \(\left(\dfrac{1}{2}xy-x\right)\left(2y+y^2-1\right)\)
\(=xy^2+\dfrac{1}{2}xy^3-\dfrac{1}{2}xy-2xy-2xy^2+x\)
\(=\dfrac{1}{2}xy^3-xy^2-\dfrac{5}{2}xy+x\)
=>Chọn D
Câu 6: \(\dfrac{9a^5b^5+4a^3b^2-5a^4b^2+2a^3b^3}{2a^3b^2}\)
\(=\dfrac{9a^5b^5}{2a^3b^2}+\dfrac{4a^3b^2}{2a^3b^2}-\dfrac{5a^4b^2}{2a^3b^2}+\dfrac{2a^3b^3}{2a^3b^2}\)
\(=\dfrac{9}{2}a^2b^3+2-\dfrac{5}{2}a+b\)
=>Chọn B
Câu 7: \(\left(x-1\right)\left(2x+5\right)-\left(1-2x+x^2\right)\left(x-5\right)\)
\(=\left(x-1\right)\left(2x+5\right)-\left(x-1\right)^2\left(x-5\right)\)
\(=\left(x-1\right)\left[\left(2x+5\right)-\left(x-1\right)\left(x-5\right)\right]\)
\(=\left(x-1\right)\left(2x+5-x^2+6x-5\right)\)
\(=\left(x-1\right)\left(-x^2+8x\right)=-x\left(x-8\right)\left(x-1\right)\)
=>Chọn C
Câu 8: \(x^2-4xy+3y^2\)
\(=x^2-xy-3xy+3y^2\)
\(=x\left(x-y\right)-3y\left(x-y\right)\)
\(=\left(x-y\right)\left(x-3y\right)\)
=>Chọn B
Câu 9: \(\left(x^2+4x-3\right)^2-5x\left(x^2+4x-3\right)+6x^2\)
\(=\left(x^2+4x-3-2x\right)\left(x^2+4x-3-3x\right)\)
\(=\left(x^2+2x-3\right)\left(x^2+x-3\right)\)
=>Chọn B
Câu 10: \(x^3+6x^2+11x+6\)
\(=x^3+x^2+5x^2+5x+6x+6\)
\(=x^2\left(x+1\right)+5x\left(x+1\right)+6\left(x+1\right)\)
\(=\left(x+1\right)\left(x^2+5x+6\right)=\left(x+1\right)\left(x+2\right)\left(x+3\right)\)
=>Chọn D
5B C đều đúng (sao 2 câu này đáp án giống nhau vậy)
6B
7C
8B, C đều đúng
9B
10D
