Question

Could you please help me out ??

Answer 1

Just remember in Law of cosines:


`a^(2) = b^(2) + c^(2) - 2bccosA`

The A there is the angle opposite of side a.

In the case of the formula given to you for triangle RST instead of A, S was used and that means the letter in the left side of the equation would be s, so S = 5.

If you look at the base formula given to you, 5 is S. With that alone you can eliminate the first three choices because none of them shows that S = 5.