Question

[không tên]

B1 : Rút gọn 

1, x ( 2x + 1 ) - x² ( x + 2 ) + ( x² - x + 3 ) 

2, 4 ( x - 6 ) - x² ( 2 + 3x ) + x ( 5x - 4 ) + 3x² ( x- 1 )

3 , ( x - 5 ) ( 2x + 3 ) - 2x ( x - 3 ) + ( x - 2 ) ( x + 5 )

B2 : Tính giá trị biểu thức 

     P = ( x² - 5 ) ( x + 3 ) - ( x + 4 ) ( x² - x ) tại x = -1

B3 Tìm x

     1 , x ( 5 - 2 x ) + 2x ( x - 1 ) = 15

     2 , ( 8x - 3 ) ( 3x + 2 ) - ( 4x + 7 ) ( x + 4 ) = ( 2x + 1 ) ( 5x - 1 )

Answer 1

[Nguyễn Văn Nam]

a) x(2x+1)-x²(x+2)+(x³-x+3)= 2x²+x-x³-2x²+x³-x+3= 3

b)x (3x²-x+5)-(2x³+3x-16)-x(x²-x+2)= 3x³-x²+5x-2x³-3x+16-x³+x²-2x= 16

Answer 2

[Nguyễn Minh Quang]

bài 1

1.\(x\left(2x+1\right)-x^2\left(x+2\right)+\left(x^2-x+3\right)=2x^2+x-x^3-2x^2+x^2-x+3=-x^3+x^2+3\)

2.\(4\left(x-6\right)-x^2\left(2+3x\right)+x\left(5x-4\right)+3x^2\left(x-1\right)=4x-24-2x^2-3x^3+5x^2-4x+3x^3-3x^2=-24\)

3.\(\left(x-5\right)\left(2x+3\right)-2x\left(x-3\right)+\left(x-2\right)\left(x+5\right)=2x^2-7x-15-2x^2+6x+x^2+3x-10=x^2+2x-25\)bài 2.

\(P=\left(1-5\right)\left(-1+3\right)-\left(-1+4\right)\left(1+1\right)=-8-6=-14\)

bài 3.

1.\(x\left(5-2x\right)+2x\left(x-1\right)=15\Leftrightarrow5x-2x^2+2x^2-2x=15\Leftrightarrow-2x=10\Leftrightarrow x=-5\)

2.\(\left(8x-3\right)\left(3x+2\right)-\left(4x+7\right)\left(x+4\right)=\left(2x+1\right)\left(5x-1\right)\)

\(\Leftrightarrow24x^2+7x-6-4x^2-23x-28=10x^2+3x-1\)

\(\Leftrightarrow10x^2-19x-33=0\Leftrightarrow10x^2-30x+11x-33=0\Leftrightarrow\left(x-3\right)\left(10x+11\right)=0\)

\(\Leftrightarrow\orbr{\begin{cases}x=3\\x=-\frac{11}{10}\end{cases}}\)