tg a = 3
sin a /cos a =3 | *cos a
sin a = 3 cos a | ( )²
sin²a = 9cos²a
sin²a / 9 (1-sin²a)
sin²a = 9 -9sin²a
10sin²a = 9 | :10
sin²a = 9/10
sin a = 3/√10
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sin a = 3cos a | :3
cos a = sin a /3
cos a = (3/√10) /3
cos a = 1/√10
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(sin a -cos a)² =
(3/√10 - 1/√10)² =(2/√10)² =4/10 =2/5 =0,4
