if x>0 and the fourth term in the expansoin of (1+3x/8)10 has maximum value ..then x lies in..........
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2 Answers
62To solve such problems..
You should try and ddo this..
find the ratio of the nth and (n+1)th terms {Take x as well in the expansion.. It depends on the question.. ilike in this questino, they have asked the 4th term.. not the coefficient of the 4th term.. so we will include x)
what that does is it gives you an idea of how terms are moving
then see where this value becomes less than 1
Once you know where the value becomes less than 1, you know where the ratio increases or decreses
I hope you can solve the rest here :)
1as the 4th term is the greatest
3<(n+1)|x|/(|x|+1)<4
we know n=10
on solving u get |x|>3/8 and |x|<4/7... take intersection... hope that this solution helps you..
