We have, (1+2x+3x2)6=r=0∑66Cr(2x+3x2)r
=6C0+6C1(2x+3x2)+6C2(2x+3x2)2+…+6C6(2x+3x2)6
∴ Coefficient of x2=18+60=78
Again, coefficient of x2 in (1−4x2)6=−24
Constant term in ((1+2x+3x2)6+(1−4x2)6) is 1+1=2.
Thus, the required coefficient of x2=2 (coefficient of x2) in ((1+2x+3x2)6+(1−4x2)6)−constant term in ((1+2x+3x2)6+(1−4x2)6)
=2(78−24)−2
=106.