所求面积=∫arcsinydy+∫arccosydy
=(yarcsiny)│-∫ydy/√(1-y²)+(yarccosy)│
+∫ydy/√(1-y²)
=√2π/8+[√(1-y²)]│-√2π/8-[√(1-y²)]│
=(√2/2-1)-(0-√2/2)
=√2-1