C= 180 - 105 - 30 =45
Δ ADC drept isoscel AD =DC =20 cm
Δ ADB drept cu mas<B =30 ⇒ AB = 2·20 cm =40 cm
BD² = AB² - AD² = 40² - 20² = 1600 -400 = 1200
BD= √12√100 = √4√3·10 = 2·10·√3 = 20√3
BC= BD+DC= 20√3 + 20 = 20 ( √3+1 )
aria = BC · AD /2 = 20(√3+1 ) ·20 /2 = 200 (√3+1) cm²