pl answer Q6 (multi option type)
pl answer Q6 (multi option type) If in expansion of (l I 5. —(1+ax)3 is ascending powers of x, the coefficients of x and .12 are both zero, then C) la-bl=3 D) la-bl=4 6. Let and x2 are two values of x for which it is known that the fourth term of the expansion loggX)6 is 14580, then : 1 9 28 9 D) Xl.X2=— 3 b 7. In the expansion of (ax + b)2009, if the coefficient ofx2 and x3 are equal, then — : A) 666 B) 667 C) 668 D) 669 213 APEX SERIES for Sri Chaitan a

Dear student 
The fourth term in the expansion of (x+xlog3x)6 is 6C3x3.(xlog3x)3=14580so, 20x3.(xlog3x)3=14580x3.(xlog3x)3=729x.xlog3x3=729x.xlog3x=9 Taking log3 both sides log3(x.xlog3x)=log39=2log3x+log3x.log3x=2(Applying logab=loga+logb and logab=bloga), we have (log3x)2+log3x-2=0(log3x-1)(log3x+2)=0log3x=-2,1x=3-2,31=19,3 so x1+x2=3+19=289, option Bis correct, and  x1. x2=13, option D is correct 
Hope this clears your doubt 
With regards 

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