If f(x) = 2x2x + 2, x R, then k=181 f ( k82 ) is equal to
- 82
- 81 2
- 41
- 812
Answer
(4) 812
Solution
f(1 - x) = 21-x21-x + 2 = 22 + 2 2x = 2 2 + 2x
f(x) + f(1 - x) = 2x + 22x + 2 = 1
Pair the terms k and 82 - k: f ( k82 ) + f ( 82 - k82 ) = 1, for k = 1, 2, , 40 40 pairs.
Middle term: f ( 4182 ) = f ( 12 ) = 2 2 + 2 = 12
Sum = 40 + 12 = 812
Answer: (4)