Question 1096119
Do polynomial division
=======x^3+x^2-1
2x-3/2x^4-x^3-3x^2-2x+a
=====2x^4-3x^3 (change signs)
==========2x^3-3x^2-2x+a 
==========2x^3-3x^2
===================-2x+a
===================-2x+3
change signs to get a-3, which must equal 0, so that a=3
then multiply the factors (2x-3)(x^3+x^2-1), which gives the original polynomial with the last term +3.