Bài 1:

\(a,3x^2-6x+9x^3=3x\left(x-2+3x^2\right)=3x\left[\left(3x^2+3x\right)-\left(2x+2\right)\right]=3x\left(x+1\right)\left(3x-2\right)\\ b,2x+2y-x^2-xy=2\left(x+y\right)-x\left(x+y\right)=\left(x+y\right)\left(2-x\right)\\ c,x^2-2x-4y^2-4y=\left(x-2y\right)\left(x+2y\right)-2\left(x+2y\right)=\left(x+2y\right)\left(x-2y-2\right)\)

\(d,x^2y-x^3-9y+9x=x^2\left(y-x\right)-9\left(y-x\right)=\left(y-x\right)\left(x^2-9\right)=\left(y-x\right)\left(x-3\right)\left(x+3\right)\\ e,x^2-25+y^2+2xy=\left(x+y\right)^2-5^2=\left(x+y-5\right)\left(x+y+5\right)\\ f,\left(x^2+1\right)^2-4x^2=\left(x^2-2x+1\right)\left(x^2+2x+1\right)=\left(x-1\right)^2\left(x+1\right)^2\)

\(g,x^2\left(x-1\right)+16\left(1-x\right)=\left(x-1\right)\left(x^2-16\right)=\left(x-1\right)\left(x-4\right)\left(x+4\right)\\ h,5x\left(x-2y\right)+2\left(2y-x\right)^2=5x\left(x-2y\right)+2\left(x-2y\right)^2=\left(x-2y\right)\left[5x+2\left(x-2y\right)\right]=\left(x-2y\right)\left(5x+2x-4y\right)=\left(x-2y\right)\left(7x-4y\right)\)

a: \(=3x\left(3x^2+x-2\right)\)

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

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

Ba is interested in playing the guitar.

Chọn A

21C; 22A

Hoa's father has less vacations than Tim's father

hoa's father has less vacations than tim's father

Hoa'father has less vacations than Tim ' father

C

c

ta có:

\(\widehat {xOy} +\widehat {x'Oy} = 180^o\) (2 góc kề bù)

mà \(\widehat {xOy} = 30^o\)

=>\(​\widehat {x'Oy} = 150^o\)

vì Ot là tia phân giác của \(\widehat {x'Oy}\)

=>\(\widehat {tOx'} = \dfrac 1 2\)\(\widehat {x'Oy}\) \(=\)\(​​\dfrac {150} 2\)\(= 75^o\)

\(=\frac{3}{2}\left(\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+......+\frac{1}{99}-\frac{1}{100}\right).\)

\(=\frac{3}{2}.\left(\frac{1}{1}-\frac{1}{100}\right)=\frac{3}{2}.\frac{99}{100}=\frac{297}{200}\)

Cảm ơn bạn