同弧所对的圆周角；同弧所对的圆周角是圆心角的；半圆（或直径）所对的圆周角是，90°的圆周角所对的弦是．

一条弧所对的圆周角等于它所对的圆心角的________．在同圆或等圆中，________弧或________弧所对的圆周角相等；直径所对的圆周角是________角，90°的圆周角所对的弦是________．

同弧所对的圆周角________；同弧所对的圆周角是圆心角的________；半圆（或直径）所对的圆周角是________，90°的圆周角所对的弦是________．