y=x－1／x的平方+2x 和f（x）=cot

y'=[(x-1)'*(x²+2x)-(x-1)*(x²+2x)']/(x²+2x)²
=[(x²+2x)-(x-1)(2x+2)]/(x²+2x)²
=(-x²+2x+2)/(x²+2x)²
f'(x)=(cosx/sinx)'
=[(cosx)'*sinx-cosx*(sinx)']/sin²x
=(-sin²x-cos²x)/sin²x
=-1/sin²x
=-csc²x

1. 2x^3y – 8xy^2=2xy(x^2-4y)
2. 9x^2y^2– 3xy + 12x^3y=xy(3xy-1+4x^2)
3. x^2- 4y^2=(x+2y)(x-2y)
4. 9a^2 – 16b^2=(3a+4b)(3-a4b)
5. x^2+ 4y^2– 4xy=(x-2y)^2
6. 9y^2 + 1 + 6y=(3y+1)^2
7. x^2– 3x – 4=(x-4)(x+1)
8. x^2+ x – 12=(x-4)(x+3)
9. x^2+ 7x – 30=(x-3)(x+10)