Answer:
x = √30
Step-by-step explanation:
From small triangle BDC:
using Pythagorean theorem
CB² = BD² + DC²
x² = BD² + 3²
Fron triangles BDC and ADB.
ΔBDC has long leg BD and short leg DC.
ΔADB has long leg AD and shirt leg BD.
AD : BD = BD : DC
7 : BD = BD : 3
7*3 = BD*BD
BD² = 7*3 = 21
x² = BD² + 3² = 21+9 = 30
x² = 30
x = √30
