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**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?