Now what is AC plus BC plus AB well that's going to be the perimeter p if you just take the sum of the sides that is the perimeter of p and it looks like we are done the area of our triangle of ABC is equal to one half times r times the perimeter which is kind of a neat result one half times the inradius times the perimeter of the triangle or sometimes we will see it written like this is equal to r times p over s oh sorry p over 2 and this term right over here the perimeter divided by 2 is sometimes called semi perimeter and sometimes it is denoted by s so sometimes you will see the area is equal to r times s where s is the semi perimeter it's the perimeter divided by 2