Solution: Let the parabola equation y=kx(x-m) and k≠0 start from the parabola crossing points o (0 0,0) and a (m m,0).

If the parabola passes through point P(m+ 1, m+ 1), then m+1= k (m+1) (m+1-m), k= 1,

Y=g(x)=x(x-m)=x2-mx，

∴f(x)=(x-n)g(x)=x(x-m)(x-n)=x3-(m+n)x2+mnx，