设直线为y=x+b,它与椭圆的交点为：x^2/3+(x+b)^2=1
x^2(4/3)+2bx+b^2-1=0,A(x1,y1),B(x2,y2)
x1+x2=-3b/2,x1x2=3(b^2-1)/4
|AB|^2=(x1-x2)^2+(y1-y2)^2=2(x1-x2)^2=2(x1+x2)^2-8x1x2=9b^2/2-6(b^2-1)=6-3b^2/2
O到AB的距离h^2=b^2/2
S为AOB面积
则S^2=1/4|AB|^2h^2=3b^2(4-b^2)/2/16
因b^2(4-b^2)