400详细OK？？？4a=3.14x2rr=2a/3.143.14x(2a/3.14)x(2a/3.14)4x314/3.14=400跟没说差不多…………神马意思？？周长相等 4a=3.14x2r圆的半径 r=2a/3.14圆的面积=πxrxr3.14x(2a/3.14)x(2a/3.14)4x314/3.14=400