Ducem DE perpendicular pe AB
In Δ ADE , dreptumghic in E :
<A = 60 gr
<E = 90 gr
⇒<D= 30 gr
cf.teoremei unghiului de 30 gr:
AE= AD/2 = 6/2 = 3 ⇒ EB = AB-3=10-3=7
DE² = AD²-AE²
DE² = 6² -3²
DE² = 27
DE = 3√3
In Δ DEB, dreptunghic in E:
BD² = DE² +EB²
BD² = (3√3)²+7²
BD² = 27+49
BD² = 76
BD = 2√19
