Найти sin a, если ctg a=-2

Question

Найти sin a, если ctg a=-2

Comments

ctg a=cos

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cos a = - 2

Answer 1

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

Comments

thanks you