(1) The relationship among sector area s, arc length l, radius r and central angle a is as follows: 2S=RL, L=aR. (2) According to the title, RL = 2, 2r+L = 4. = = > R= 1，L=2。 = = = = = & gt； A=2 (radian) (3) In the triangle AOB, it is obtained by cosine theorem: | AB | 2 = R2+R2-2r * rcos2 = 2-2cos2 = 2 (1-cos2) = 4 (sin1) 6544. |AB|=2sin 1。