y=4-x^2=0,得x=-2,x=2
与x轴所围成的平面图形的面积=∫(-2,2)（4-x^2)dx=(4x-x^3/3)|(-2,2)
=(4*2-2^3/3)-(4*(-2)-(-2)^3/3)
=16/3+16/3
=32/3