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一、填空题 (每小题 3分 ,满分 3 0分 )1 .规定 :a b=ab + ba,那么 1 4=.2 .在半径为R的⊙O中 ,弦AB=R ,弦CD=3R ,若AB∥CD ,则AB和CD间的距离是 .3 .已知∠A、∠B的两条边分别平行 ,且∠A的度数是∠B的度数的 2倍少 3 0°,则∠B的度数为 .4.如图 ,已知点E为矩形ABCD内的任意
First, fill in the blanks (3 points for each question, out of 30 points) 1. Provisions: ab = ab + ba, then 1 4 = .2. In the radius of R ⊙ O, the string AB = R, string CD = 3R, if AB∥CD, then the distance between AB and CD is .3. The two sides of known ∠A and ∠B are respectively parallel, and the degree of ∠A is 2 times less than 度B, which is less than 3°. Then, the degree of ∠B is .4. As shown in the figure, the known point E is arbitrary within the rectangle ABCD.