c) 1/2 x^3 (2x - 1) (1/4x + 1) = 1/5 x^5 - 7/4 x^4 - 1/2 x^3

c) 12x32x−114x+1

=12x3.2x−12x3.114x+1

=x4−12x314x+1

=x4.14x+1−12x3.14x+1

=x4.14x+x4.1−12x3.14x−12x3.1

=14x5+x4−18x4−12x3

=14x5+x4−18x4−12x3

=14x5+78x4−12x3.

Do đó phát biểu c) là sai.