After the value of formula 2 is brought in, sinBsinC= 1 is obtained.
Solve this formula and formula 2 at the same time, and you can get sinB=sinC= 1/2.
In fact, there are many such problems on the Internet, but only a little change in numerical value is different. I suggest you search for a few questions to consolidate, go in and ask the answer home page, and you can probably find many similar questions by typing.