First of all, let's recall the area of a triangle, knowing its base (b) and height (h):

The exercise is showing you that, if you inscribe a polynomial with more and more side, the area of the polynomial will approximate the area of the circle better and better (you can see youself that the polygon is "filling" the circle more and more as the number of sides increase).
Now, the second column tells you the area of each of the triangles the polygon is split into. So, we can see that the first polygon is split into 3 triangles, each of them having base 1.73 and height 0.5.
So, the area of each triangle is

There are three of these triangles, so the area of the whole polygon is

In the second case, you have six triangles, each with base 1 and height 0.87. So, the whole area is

Finally, in the last case you have 8 triangles, each with base 0.77 and height 0.92. So, the whole area is

Answer:
90+30=120
180-120=60 this is degree measure
Answer:
119
Step-by-step explanation:
Angle C= 62
So you add 62 + 57 which gives you 119
All angles must add up to 180 so you subtract 119 from 180 which gives you 61
Since angle A is 61 and a straight line angle is 180 you subtract 61 from 180 to give you angle B
180 - 61 = 119
therefore your answer is 119