With and , what can be said about the above inequality.
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In ( 0 ; 6 π ) both s i n x and t a n x increase. So now consider the L H S L H S < s i n ( 6 π ) + t a n 2 ( 6 π ) + s i n 3 ( 6 π ) + t a n 4 ( 6 π ) + . . . + s i n 2 n − 1 ( 6 π ) + t a n 2 n ( 6 π ) The above R H S equals to 2 1 + ( 3 1 ) 2 + . . . + ( 2 1 ) 2 n − 1 + ( 3 1 ) 2 n Now we consider these following sum A = 2 1 + ( 2 1 ) 3 + . . . + ( 2 1 ) 2 n − 1 and B = ( 3 1 ) 2 + ( 3 1 ) 4 + . . . + ( 3 1 ) 2 n . We see that ( 2 1 ) 2 A = ( 2 1 ) 3 + ( 2 1 ) 5 . . . + ( 2 1 ) 2 n + 1 ( 3 1 ) 2 B = ( 3 1 ) 4 + ( 3 1 ) 6 . . . + ( 3 1 ) 2 n + 2 Therefore A − 4 1 A = 2 1 − ( 2 1 ) 2 n + 1 ⇒ A = 3 4 [ 2 1 − ( 2 1 ) 2 n + 1 ] < 3 4 . 2 1 = 3 2 B − 3 1 B = 3 1 − ( 3 1 ) 2 n + 2 ⇒ B = 2 3 [ 3 1 − ( 3 1 ) 2 n + 2 ] < 2 3 . 2 1 = 2 1 So L H S < A + B < 3 2 + 2 1 = 6 7 < 2 , the correct choice is "False for all n ".