Law of sines. someone explain to me how to do this

  0.5 cm

Step-by-step explanation:

You are given angles B and C and side b, so you can put those values into the given equation:

  sin(105°)/(2 cm) = sin(15°)/c

Multiply this equation by c·(2 cm)/sin(105°) and you get ...

  c = (2 cm)·sin(15°)/sin(105°) ≈ 0.535898 cm

  c ≈ 0.5 cm

Comment on the given equation

When using the Law of Sines to find side lengths, I prefer to write the proportion in a form with the side length of interest in the numerator:

  b/sin(B) = c/sin(C)

or

  c/b = sin(C)/sin(B)

Using either of these forms, it is one step to find the value of c: Multiply the equation by the inverse of the coefficient of c.

  c = b·sin(C)/sin(B)