It is a triangle inside a circle..
Notice both sides of the triangle (Left and right) are radii of the circle so they are equal in length.
The angle 120 is between both sides (4cm each)
If we want the area, there is 2 ways to find it..
We can really just constract a right angle triangle from the 120 degrees and use trig to find the rest.
Other method (I prefer) Is to find the opposite side of 120 degrees, and then apply Heron's formula.
First of all let's label the sides
Let the side opposite to angle 120 be c,
Let the side on the left be b,
Let the side on the right be a.
Using the law of cosines, we know that:
c^2=a^2+b^2-2ab*cos(x) , Let the angle 120=x
So just applying the formula we get,
c^2=16+16-32*cos(120)
cos(120)=-0.5
32-32(-0.5)=48
c^2=48
c=sqrt(48) Positive or negative but since we are finding a side it must be positive.
Now let's apply heron's formula
which is:
Area=sqrt((s(s-a)(s-b)(s-c)) where s=(a+b+c)/2
we know that,
a=4
b=4
c=sqrt(48)
adding these together we get:
4+4+sqrt(48) =14.928203 approx.=15
so s=15
just subsituiting,
sqrt((15(15-4)(15-4)(15-sqrt(48))=121.038469 approx=121
So the area is 121 cm^2
I am pretty sure there is a faster solution.
Maybe using inscribed theorem etc..