(1) If CE= 1/2CB, CF= 1/2CD.

As we all know, the areas of triangle OBE, QEC, OFC and OFD are all equal.

From the area of the triangle BCF is 1/4, we can know that the area of each triangle above is112.

So the area of the quadrilateral is1-4 *112 = 2/3.

(2) If CE= 1/nCB, then CF= 1/nCD.

According to the law of (1), the triangle OEC = OFC =1(n-1) OBE =1/(n-1) ofd.

So1/(n-1) OBE * 2+OBE =1/4.

The area of OBE =(n- 1)/4*(n+ 1)

The area of the quadrilateral =1-2 (n-1)/4 * (n+1)-2/4 * (n+1).

Simplify yourself. It says I'm tired.