Hi Stephanie,

If I understand this correctly you have the matrix and you are to find its inverse. That is you want to find the matrix so that

Thus the first row times the first column must be 1, that is

a + c tan(θ/2) = 1

and the second row times the first column is 0, so

-a tan(θ/2) + c = 0

This gives you two equations in two unknowns which you can solve for a and c. Likewise multiply the first row time the second column and the second row times the second column to obtain equations in b and d.

I hope this helps,
Penny