Ctg1ctg2ctg3...ctg89=? Всё в градусах.
Ctg1⁰·ctg2⁰.....ctg88⁰·ctg89⁰=ctg1⁰·ctg2⁰...ctg44⁰·ctg45⁰·ctg(90⁰-44⁰)...ctg(90⁰-1⁰)= =ctg1⁰·ctg2⁰.....ctg44⁰·ctg45⁰·tg44⁰tg43⁰....tg1⁰=ctg1⁰·tg1⁰ctg2⁰·tg2⁰...ctg45⁰=1