In triangle mnp, m = 5 cm, n = 4 cm, and p = 8 cm. which formula can you use to find p?

8² = 4² + 5² - 2(4)(5) cos(P)
which is the third option

Explanation:
The general rule of cosine is:
a² = b² + c² - 2bc*cos(A)

In our triangle:
a is substituted by p = 8 cm
b is substituted by n = 4 cm
c is substituted by m = 5 cm
A is substituted by P which we want to find

Replace the variables in the general equation with the givens as follows:
p² = n² + m² - 2mn*cos(P)
8² = 4² + 5² - 2(4)(5) cos(P)

Hope this helps :)

The answer to that is 6