Question

On which triangle can the law of cosines be applied once to find an unknown angle measure? Law of cosines: a2 = b2 + c2 – 2bccos(A)

options are in the pics

Answer 1

I think it's D but don't quote me on that

Answer 2

Answer: The correct option is 4.

Step-by-step explanation:

The formula of law of cosine is,

`a^2=b^2+c^2-2bc\cos(A)`

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.