-5:-10:9:1.1:3:1.414:8a-6b:120:30
解:(1)①(-2)+(-3)=-5,②(-2)×5=-10,③(-3)2=9;
(2)要根据要求保留三位小数,
√1.21
=1.1,3√27
=3,√2
≈1.414;
(3)3a+2b+5a-8b
=(3a+5b)+(2b-8b)
=8a-6b;
(4)∠AOD=(180°-∠AOC)=(180°-60°)=120°,
∵∠AOC与∠DOB互为对顶角,OP平分∠BOD,
∴∠DOP=∠BOD=30°;
(5)解:移项,得3x-x=1+7
合并,得2x=8
∴x=4.