)n,x≠0,n∈N, Sum of coefficients of first three terms ‌‌nC0−‌nC1⋅3+‌nC232=376 ‌⇒3n2−5n−250=0 ‌⇒(n−10)(3n+25)=0 ‌⇒n=10 Now general term ‌10Crx10−r(‌
−3
x2
)r ‌=‌10Crx10−r(−3)r⋅x−2r ‌=‌10Cr(−3)r⋅x10−3r Coefficient of x4⇒10−3r=4 ‌⇒r=2 ‌‌10C2(−3)2=405