minta bantuannya dong

Kubus ABCD.EFGH
Misal : rusuk = 2a

S titik tengah PQ
PQ = a√2
HS = PS = 1/2 PQ = 1/2 a √2

Titik pertemuan g1 dan g2 --> R
Titik tengah AC = O
HS/HO = HR/RD = 1/2
HR = 2a

RS = √(HR² + HS²)
RS = √(4a² + 1/2 a²)
RS = (3/2)a√2

sudut PRS = 1/2 θ

tan 1/2 θ = PS/RS = (1/2 a√2)/(3/2 a√2)
tan 1/2 θ = 1/3 --> opsi A


Coba gambar sendiri ya... :)