Odpowiedzi

2010-02-25T19:46:20+01:00
2010-02-25T19:50:06+01:00
Sin²α + cos²α = 1
cos²α = 1 - sin²α
cos²α = 1 - (2/7)²
cos²α = 1 - 4/49
cos²α = 45/49
cosα = √45/49
cosα = 3√5/7