1) S = S¹+S²
S¹ = 3²+5² = 9+25=34 cm²
S² = 5²+9²= 25+81=106 cm²
S=34+106=140cm²
2)c²=a²+b²=12²+9²=144+81=225 cm²; c=√225 = 15 cm
3)18:2=9 cm
b²=c²-a²= 15²-9²=225-81=144 cm²; b=√144=12 cm
4)AO= 40:2 = 20 cm
BO²= AB² - AO² = 25²-20²=625-400 = 225cm²; BO = √225=15 cm.
BO=OD=15cm
BD=15*2=30 cm