limas beraturan
AB = AD = 4 cm
AT = 5 cm
cos DBT
= (DB² + BT² – DT²)/(2 . DB . BT)
= ((4√2)² + 5² – 5²)/(2 . 4√2 . 5)
= (4√2)² / (2 . 4√2 . 5)
= 4√2 /10
= 2/5 √2
sin DBT = √(1 – cos² DBT) = 1/5 √17
Jarak D ke TB
= DX
= DB sin DBT
= 4√2 × 1/5 √17
= 4/5 √34 cm