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Questions  

 If the 4th  term in the expansion of 2+3x810 has the maximum numerical value, then the range of values of x for which this will be true is 

a
−6421
b
2164
c
−6421
d
−2164

detailed solution

Correct option is A

T4 is numerically greatest term ⇒T4 T3>1,⇒T4 T5>1⇒T4 T3>1,T5 T4<1Now T4 T3=C3   10273x83C2   10283x82=x2,T5 T4=C4   10263x84C3   10273x83=21x64∴T4 T3>1⇒x2>1⇒|x|>2⇒x∈-∞,-2∪2,∞  →1and T5 T4<1⇒21x64<1⇒|x|<6421⇒x∈-6421,6421  →2By 1 and 2 we have x∈−6421,−2∪2,6421

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f the coefficient of the 5th term be the numerically the greatest coefficient in the expansion of (1x)n, then the positive integral value of n, is 


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