✔ 最佳答案
As ∫(x→(x+pi)) |sinx| dx = 2 for all x,
∫(0→n) |sinx| dx = n*2/pi + constant error
The error is constant because the line y = 2x/pi is asymtopically equal to the integral f(x) = ∫(0→x) |sin u| du. f(x) - 2x/pi is periodic and checking the first period all points are definite.
Write
∫(0→n) |sinx| dx = 2n/pi + O(1) as x goes to infinity.
Now
lim(n→∞) ∫(1→n) |sinx|/n dx
= lim(n→∞)((1/n)( ∫(1→n) |sinx| dx ))
= lim(n→∞)((1/n)( ∫(0→n) |sinx| dx ) - (1/n)( ∫(0→1) |sinx| dx ))
As in the second term the integral converges but with 1/n in front of it it's certainly zero.
= lim(n→∞)((1/n)( ∫(0→n) |sinx| dx ))
= lim(n→∞)((1/n)(2n/pi + O(1)))
= lim(n→∞)(2/pi + O(n^-1))
As n -> infinity, O(n^-1) goes to zero.
= 2/pi.
If you don't like to use the big-O notation just sandwich the constant error and the result is the same.