∫0∞dx1+x2=limb→∞∫0bdx1+x2 ∫0∞dx1+x2=limb→∞tan-1x0b ∫0∞dx1+x2=limb→∞tan-1b - tan-10 ∫0∞dx1+x2=tan-1∞ - tan-10 ∫0∞dx1+x2=π2