Get clear, concise, and accurate answers to your questions on IDNLearn.com. Our community is ready to provide in-depth answers and practical solutions to any questions you may have.
See my answer to your other question for more details (26127939).
We found that cos(a) = 4/5 and sin(b) = 35/37. Then
cos(a + b) = cos(a) cos(b) - sin(a) sin(b)
cos(a + b) = 2/37 • 4/5 - 3/5 • 35/37
cos(a + b) = -57/185