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43. ∫<-1, 1> f(x)dx 必为常数, 设为 A, 则
f(x) = (1+sinx)/(1+x^2) - A
两边在 [-1, 1] 上积分,注意左边是 A, 得
A = ∫<-1, 1> [(1+sinx)/(1+x^2)]dx - A[1-(-1)]
3A = ∫<-1, 1> [1/(1+x^2)]dx + ∫<-1, 1> [sinx/(1+x^2)]dx
= [arctanx]<-1, 1> + 0 = π/2,
A = π/6, f(x) = (1+sinx)/(1+x^2) - π/6
lim<x→∞>f(x) = lim<x→∞>[(1+sinx)/(1+x^2) - π/6] = -π/6
f(x) = (1+sinx)/(1+x^2) - A
两边在 [-1, 1] 上积分,注意左边是 A, 得
A = ∫<-1, 1> [(1+sinx)/(1+x^2)]dx - A[1-(-1)]
3A = ∫<-1, 1> [1/(1+x^2)]dx + ∫<-1, 1> [sinx/(1+x^2)]dx
= [arctanx]<-1, 1> + 0 = π/2,
A = π/6, f(x) = (1+sinx)/(1+x^2) - π/6
lim<x→∞>f(x) = lim<x→∞>[(1+sinx)/(1+x^2) - π/6] = -π/6
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