Use the Law of Cosines to write an expression equivalent to z.

  see below

Step-by-step explanation:

The pattern you're trying to match is ...

The first term (a) must match x^2.

The last term (bc) must match 2xy·cos(Z). Since one of the tiles is cos(z), assigning that to "c" will leave "b" = 2xy, another tile. Hence the solution shown below. (Note that values of "b" and "c" could be swapped and the equation would still be correct, even if the form doesn't quite match.)