1) а)-21b^3-14b^2=-7b^2(3b+2)
б)mn+3m-n^2-3n=(mn+3m)-(n^2+3n)=m(n+3)-n(n+3)=(n+3)(m-n)
в)81a^2-b^2=(9a-b)(9a+b)
г)3y^3-36y^2+108y=3y(y^2-12y+36)
3)(x+2)^2-49=0
x^2+4x+4-49=0
x^2+4x-45=0
D=16+180=196
x1=-4+14/2=5
x2=-4-14/2=-9
Ответ:-9;5
4)x^2+14x-51=(x+17)(x-3)
x^2+14X-51=x^2-3x+17x-51
x^2+14x-51=x^2+14x-51