Merge similar items, a (1-COSA/Sina) = b (cosb/sinb-1).

According to sine theorem a/b=sinA/sinB

Get: cosB-sinB=sinA-cosA (use it to simplify yourself)

According to the sum and difference formula of two angles, the root number 2 is extracted from both sides.

Root number 2 (SIN 45 COSB-COS 45 SINB) = Root number 2 (SINA COS 45-COSAS IN 45).

Namely: sin (45-b) = sin (a-45)

So: 45-B = A-45 or 45-B+A-45 = 180 (omitted).

So a+b = 90, which means c = 90.