Question #e6972

1 Answer
Manasvini Nittala
Jan 22, 2018

# T_3=135a^4b^2#

Explanation:

the given expansion #(a-3b)^6# is of the for #(x-a)^n#
#r^(th)term # in this expression is given as
#T_(r+1)=(-1)^r.""_r^nC .(x)^(n-r).a^r#
here #x=a,a=3b#
we require the #3^(rd)termrArrr=2#
substituting in the formula we get
#T_3=(-1)^2.""_2^6C.(a)^(6-2).(3b)^2#
#rArr15.a^4.9.b^2rArr135a^4b^2#
#:. T_3=135a^4b^2#

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