clearly (1-3x)(x+4) is not equal to 2-11/2 x -1.5×2.
after using mode 3, 3 to get the roots of the quad eq, you have to check that yr factorisation is correct. There are many ways of writing a quad expression with the same roots.
For such binomial questions, i would suggest you to expand the expression in part (i) and part (ii) and see how it is related to the later binomial expansion. In this question, when you expand (1-3x)(2+x/2), you will get 2-11/2x -3×2/2. Then you can proceed with your solution.
If this is a emaths question on factorisation (2-11/2 x -3/2 x2), you can do in as follow:
2-11/2x -3/2×2 =-1/2(3×2+11x-4)=-1/2(x+4)(3x-1).
ps…hope you can understand. Do not know how to type the power using hp.