math test revision

1 (a)show that the graph of quadratic function y=-mx^2+(2m+n)x+2n cuts the x axis at 2 distinct points if m and n have the same sign.

(b)suppose alpha and beter are the roots of the quadratic equation as the same as that in (a). if the sum of the cube of the roots is 10n/m+5n^2/m^2,show that (m+n)(2m+n)(4m+n)=0.0

omg and who can teach me the techniques of doing such questions?i always cannot look through the tricky points in the questions and it really upsets me! it seems like i cannot improve even if i did a lot exercises! i am frustrated ! should i give up?������������