---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- Let g(t) = log(1+t)/(1+t^2). We calculate the defined integral of g on [0,1]. Then we look for the integral on [-1,0]. Let's see if we can even calculate the one between -1 and ∞. We plot the graph of x -> ∫[0,x]g from -1 to ∞ (which we could have traced first, to orient ourselves in the previous calculations). g <- function(t) log(1+t)/(1+t^2) integral(g, 0,1) # [1] 0.2721983 # Try to see with WoframAlpha if it is an approximation of a simpler term: # I introduce 0.2721983 and get log(2)·π/8. I control: log(2)*pi/8 # [1] 0.2721983 OK integral(g, -1,0) # [1] -0.6437673 # To compute the integral between -1 and ∞, it is best to use the expression of the # integral between successive powers of 10: h = function(n) integral(g,10^n,10^(n+1)) integral(g, -1,1) # [1] -0.3715691 integral(g, -1,1)+h(0) # [1] 0.4823926 # integral(g, -1,1)+h(0)+h(1) # [1] 0.7604949 integral(g, -1,1)+h(0)+h(1)+h(2)+h(3)+h(4)+h(5) # [1] 0.81658 integral(g, -1,1)+h(0)+h(1)+h(2)+h(3)+h(4)+h(5)+h(6) # [1] 0.8165931 integral(g, -1,1)+h(0)+h(1)+h(2)+h(3)+h(4)+h(5)+h(6)+h(7) # [1] 0.8165946 integral(g, -1,1)+h(0)+h(1)+h(2)+h(3)+h(4)+h(5)+h(6)+h(7)+h(8) [1] 0.8165948 # With WolframAlpha I see that it equates to log(2)·π·3/8 # Graph of 0∫xg BF=4; HF=2.5 Plane(-1,20, 0,1.5) Gintegra(g, 0,-1, "blue") Gintegra(g, 0,20, "brown") (In some analysis manuals as 0∫xg log(1+x^2)·atn(x)/2 is determined; it coincides with the exact expression only for x = 1: this testifies how useful it is to make such calculations even with the help of the computer!)