f ( x ) = ∫ 0 1 t ∣ t − x ∣ d t
If the minimum value of f ( x ) above, where x ∈ R , is ω , what is the value of ⌊ 1 0 0 0 ω ⌋ ?
This section requires Javascript.
You are seeing this because something didn't load right. We suggest you, (a) try
refreshing the page, (b) enabling javascript if it is disabled on your browser and,
finally, (c)
loading the
non-javascript version of this page
. We're sorry about the hassle.
How can we assume that x lies between 0 and 1? Doesn't t lie in that interval?
Log in to reply
Take the case of x lying outside the interval. The value of integral turns out to be less than the answer.
Note that f ( x ) = ∫ 0 1 t ∣ t − x ∣ d t = ⎩ ⎪ ⎪ ⎨ ⎪ ⎪ ⎧ ∫ 0 1 t ( t − x ) d t ∫ 0 1 t ( x − t ) d t for x < t for x ≥ t
For x ≤ 0 , f ( x ) = ∫ 0 1 t ( t − x ) d t = 3 1 − 2 x ⟹ min ( f ( x ) ) = f ( 0 ) = 3 1 .
For x ≥ 0 , f ( x ) = ∫ 0 1 t ( x − t ) d t = 2 x − 3 1 ⟹ min ( f ( x ) ) = f ( 1 ) = 6 1 .
For 0 < x < 1 ,
f ( x ) ⟹ f ′ ( x ) x ⟹ min ( f ( x ) ) = ∫ 0 1 t ∣ t − x ∣ d t = t < x ∫ 0 x t ( x − t ) d t + t > x ∫ x 1 t ( t − x ) d t = 2 x 3 − 3 x 3 + 3 1 − 2 x − 3 x 3 + 2 x 3 = 3 x 3 − 2 x + 3 1 = x 2 − 2 1 = 2 1 = f ( 2 1 ) = 6 2 − 2 ≈ 0 . 0 9 7 6 3 1 Equating to 0 Since 0 < x < 1 Since f ′ ′ ( 2 1 ) > 0
Therefore, ⌊ 1 0 0 0 ω ⌋ = 9 7 .
Problem Loading...
Note Loading...
Set Loading...
The given integral is:- f ( x ) = ∫ 0 1 t ∣ t − x ∣ d t This can be broken into two parts. (Here we assume that x lies between 0 and 1 ):- f ( x ) = ∫ 0 x t ( x − t ) d t + ∫ x 1 t ( t − x ) d t Solving the above integral we get:- f ( x ) = 3 x 3 − 2 x + 3 1 Differentiating w.r.t. x :- f ′ ( x ) = x 2 − 2 1 For minima, f ′ ( x ) = 0 x 2 = 2 1 x = 2 1 Hence, f ( x ) = 6 2 1 − 2 2 1 + 3 1 Hence, f ( x ) = 6 2 − 2 Therefore:- ω = 0 . 0 9 7 6 3 1