5.3.2.29 Various Problems in the Space

Condition: through the top of the direct angle \ (C \), an isosceles rectangular triangle \ (a b c \) a plane \ (\ alpha \) was carried out so that \ (\ alpha \) is parallel to the hypotenuse and makes an angle of 30 ° degrees. Find the angle between the plane \ (a b c \) and \ (\ alpha \).