2m^3-4m^2+2m 因式分解

若x+y=0,xy=-7,则
x^2y+xy^2
=xy(x+y)=0 ,
x^2+y^2=(x+y)²-2xy
=14
已知a+b=2,ab=2,则
2分之1a^3b+a^2b^2+2分之1ab^3
=1/2ab(a²+2ab+b²)
=1/2ab(a+b)²
=1/2*2*2²
=4
已知a+b=-5,ab=7,则
a^2b+ab^2-a-b
=ab(a+b)-(a+b)
=-35+5
=-30
（-2）^2n+1+2（-2）^2n
=-2^(2n+1)+2*2^2n
=-2^(2n+1)+2^(2n+1)
=0