1.

Find the middle the terms in the expansion of `(5x-7y)^(7)`

Answer» Since n is an odd number, the expansion contains two middle terms
`((7+1)/(2))th and ((7+3)/(2))` th terms are the two middle terms in the expansion of `(5x-7y)^(7)`
`t_(4)=T_(3+1)=(-1)^(3)""^(7)C_(3)(5x)^(7-3)(7y)^(3) =-""^(7)C_(3)(5x)^(4)(7y)^(3)`
=`T_(5)=T_(4+1)=(-1)^(4)*""^(7)C_(4)(5x)^(7-4)*(7y)^(4)=""^(7)C_(4)(5x)^(3)(7y)^(4)`


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