Let e be the base of natural logarithm and let f : \1, 2, 3, 4\ \1, e, e2, e3 \ and g : \1, e, e2, e3 \ \1, 12, 13, 14 \ be two bijective functions such that f is strictly decreasing and g is strictly increasing. If (x)= [f-1 \g-1 ( 12 ) \ ]x, then the area of the region R= \(x, y) : x2 y (x), . . 0 x 1 \ is :
- 3- e(2)3 e(2)
- 13 e(2)
- 3+ e(2)
- 3+ e(2)2+ e(3)
Answer
(1) 3- e(2)3 e(2)
Solution
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f is strictly decreasing, so f(1) = e3, f(2) = e2, f(3) = e, f(4) = 1.
g is strictly increasing and 14 < 13 < 12 < 1, so g(1) = 14, g(e) = 13, g (e2 ) = 12, g (e3 ) = 1.
Hence g-1 ( 12 ) = e2 and f-1 (e2 ) = 2, which gives (x) = 2x.
For 0 x 1, 2x 1 x2, so R lies between y = x2 (below) and y = 2x (above):
Area = 01 (2x - x2 )dx = [ 2x e 2 - x33 ]01
= 2 - 1 e 2 - 13 = 3 - e(2)3 e(2)
Answer: (1)