Some of my ____ (friend) drink orange juice.
①(2x+1)2=3(2x+1)
②4(x﹣1)2﹣9(3﹣2x)2=0.
(I)求证:平面SAB⊥平面SAC;
(II)求二面角B﹣SC﹣A的余弦值.
亚洲地势的特点是( )