)7 ∴ General term Tr+1=‌7Cr⋅(xn)7−r⋅(‌
2
x5
)r =‌7Cr⋅x7n−nr−5r⋅2r For positive power of x, 7n−nr−5r>0 ⇒7n>r(n+5) ⇒r<‌
7n
n+5
As r represent term of binomial expression so r is always integer. Given that sum of coefficient is 939. When r=0, sum of coefficient =‌7C0⋅20=1 when r=1, sum of coefficient =‌7C0⋅20+‌7C1⋅21=1+14=15 when r=2, sum of coefficient =‌7C0⋅20+‌7C1⋅21+‌7C2⋅22 =1+14+84 =99 when r=3, sum of coefficient =‌7C0⋅20+‌7C1⋅21+‌7C2⋅22+‌7C3⋅23 =1+14+84+280 =379 when r=4, sum of coefficient =‌7C0⋅20+‌7C1⋅21+‌7C2⋅22+‌7C3⋅23+‌7C4⋅24 =1+14+84+280+560 =939 To get value of r=4, value of ‌