2х(х-3)-3х(х+5)= (2х^2-6x)-(3x^2+15x)=2x^2-6x-3x^2-15x=-x^2-21x
(a+7)(a-1)+(a-3)2=(a^2-a+7a-7)+(2a-6)=a^2-a+7a-7+2a-6=a^2+8a-13
3(y+5)^2-3y^2=3(y^2+10y+25)-3y^2=3y^2+10y+25-3y^2=10y+25
1) xy²+x²y³=xy²*(1+xy)
2)
b²-a²
=a²b²*(a²-b²)=a²b²*(a-b)*(a+b)
3) m²n²+mn³=mn²*(m+n)