lim(x->∞)[∫(arctant)²dt/√(1+x²)]
=lim(x->∞){(arctanx)²/[x/√(1+x²)]}
={lim(x->∞)[(arctanx)²]}*{lim(x->∞)[√(1/x²+1)]}
=(π/2)²*√(0+1)
=π²/4.
lim(x->∞)[∫(arctant)²dt/√(1+x²)]
=lim(x->∞){(arctanx)²/[x/√(1+x²)]}
={lim(x->∞)[(arctanx)²]}*{lim(x->∞)[√(1/x²+1)]}
=(π/2)²*√(0+1)
=π²/4.