I have prob getting other two factors.
Had solved that (x-1) is a factor of 2X^3+5X^2-11X+4.
2X^3+5X^2-11X+4
=2(1)^3+5(1)^2-11(1)+4
=0
You appear to be assuming that the other factor is . Why?
If you insist upon that method (though ordinary division or synthetic division is simpler) you need to write . Do the multiplication and combine like powers and you will get three equations for a, b, and c. (Actually, you get 4 equations but they are not "independent" since x-1 is a factor of .