If U = {all positive integers}

1, 2, 3, and etc

Step-by-step explanation: They are 3 type or integers, +, - and 0+ is the set of all positive integers 1, 2, 3 and etc, while - is the set of all negative integers -1, -2, -3, etc. Zero has its own set.

where is the triangle?

answer: 0

step-by-step explanation: the positive, like 5, + its opposite, like -5 would be 0

5+(-5)=0, or 5-5=0