Questions
The two consecutive terms in the expansion of (3x + 2)74, whose coefficients are equal, are
a
20th and 21st
b
30th and 31st
c
40th and 41st
d
none of these
detailed solution
Correct option is A
Since, T3T2=7 (given)⇒ nC22xn−24−x2 nC12xn−1⋅4−x=7⇒ n−12⋅12x3=7Also, nC2+nC1=36⇒ n(n−1)2+n=36⇒ n2+n−72=0⇒ n=8,−9n = – 9 is not possible as in Eq. (1), n – 1 should be positive.Substituting n = 8 in Eq. (1), we get23x=12=2−1⇒ 3x=−1⇒ x=−13Talk to our academic expert!
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