趣味英语。Helen’s friend has eight animals.They are rabbits and ducks.They have twenty-eight feet(脚).So,there are ________ rabbits and ________ ducks.
已知向量与的夹角是,且,,若,则实数等于( )
已知点在函数的图象上,则的值等于( )
已知为纯虚数,则( )
已知,,则( )
若,则的值为( C )