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Questions  

 Let a>2 be a constant. If there are just 18 positive integers  satisfying the inequality (xa)(x2a)xa2<0 then  the value of a is 

a
4
b
5
c
6
d
7

detailed solution

Correct option is B

as a>2 hence a2>2a>a>2 now (x−a)(x−2a)x−a2<0⇒ the solution set is as shown     between (0,a) there are (a−1) positive integers  and between (2a,a2), there are a2 -1-2a positive integers∴ a2−1-2a+a−1=18⇒a2−a−20=0⇒(a−5)(a+4)=0∴ a=5

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