Answer: The correct option is 4.
Explanation:
The formula of law of cosine is,
[tex]a^2=b^2+c^2-2bc\cos(A)[/tex]
Where a,b,c are sides of the triangle and A is the interior angle of vertex A.
Reason for correct option:
From the above formula we can easily conclude that to find an unknown angle measure we need the length of all sides of the triangle.
In figure 4 all sides are given, so the correct option is 4.
Reason for incorrect option:
In figure 1,2 and three all sides are not known, so we can apply the cosine rule to mind the unknown angle measure.
Therefore option 1,2 and 3 are incorrect.
