Найдите sinA, если:а)ctgA =2; ctgA =1/3

ctg(a) = cos(a)/sin(a)

cos(a)/sin(a) = -2

cos(a) = -2sin(a)

cos²(a) + sin²(a) = 1

(-2sin(a)² + sin²(a) = 1

4sin²(a) + sin²(a) = 1

sin²(a) = 1/5

sin(a) = √1/5