Calculate some things about a tetrahedron

[Harmony]

Question Statement:
Each surface of a tetrahedron ABCD is an equilateral triangle with each side 2 units long. The midpoint of AB and CD are L and M respectively. Calculate, by giving your answers correct to 3 s.f. or to the nearest 0.1 degree,

a) The length of the perpendicular from A to the plane BCD
b) The angle between the surface ACD and BCD
c) Angle between AB and the plane BCD

My Attempt So Far :
I have solved part A and B. The only part that confuse me is part C.
My calculation :
let the angle between AB and the plane BCD be x.
The perpendicular distance from A to the plane BCD be p.
So sin x = p/AB = 1.63/2

But the answer given is x = 53.1 degree, which is slightly smaller than the answer I found.

Is the method I used wrong?

 

[Stevedye56]

Just looking quickly the answer you have may be less due to rounding error. How much less is your answer than the answer given in the book?

 

[Harmony]

1 degree. The answer given is 53.1 degree, wheres mine is about 54 degrees.