Odpowiedź:
sinα = 0,4 =4/10
sin²α = (4/10)² = 16/100
1 - cos²α= 16/100
cos²α= 1 - 16/100 = 84/100
cosα = √(84/100) = √(4 * 21)/10 = 2√21/10
tgα = sinα/cosα = 4/10 : 2√21/10 = 4/10 * 10/2√21 = 4/2√21 =
= 4√21/(2* 21) = 4√21/42 = 2√21/21 ≠ 4 ,więc nie ma takiego kąta ostrego
