Question

Дано: ctgb-11/3 Найдите cosb

Answer 1

1+ctg^2 b=1/sin^2 b
1+121/9=1/sin^2 b
130/9=1/1/sin^2 b
sin^2 b=9/130
sin^2 b+cos^2 b=1
cos^2 b=1-sin^2 b
cos^2 b=1-9/121=112/121
cos b=($\frac{ \sqrt{112}}{11}$)/11