Answer:
To one decimal place, x = 7.7 cm
Step-by-step Step-by-step explanation:
Let y equal BD.
Since AD is a bisector of angle BAC, angle DAB is 17°.
tan(17°) = y/21, so y = 21 tan(17°)
tan(34°) = (x + 21 tan(17°))/21
21 tan(34°) = x + 21 tan(17°)
x = 21(tan(34°) - tan(17°)) = 7.7 cm