‌(1+2x+3x2)10 ‌‌=a0+a1x+a2x2+...+a20x20 ={1+x(2+3x)}10 Then by binomial expansion =‌10C0+‌10C1x(2+3x)+‌10C2x2(2+3x)2+... Now, the coefficient of x in this expansion ie, ‌‌a1=2⋅10=20 and the coefficient of x2 in this expansion =3⋅‌10C1+4⋅‌10C2 iea2=3⋅10+4⋅45 =30+180 =210 So, ‌‌‌