Find værdien af theta, hvis Cos (theta) / 1 - sin (theta) + cos (theta) / 1 + sin (theta) = 4?
Theta = pi / 3 eller 60 ^ @ Okay. Vi har: costheta / (1-sintheta) + costheta / (1 + sintheta) = 4 Lad os ignorere RHS for nu. costheta / (1-sintheta) + costheta / (1 + sintheta) (costheta (1 + sintheta) + costheta (1-sintheta)) ((1-sintheta) (1 + sintheta) ) + (1 + sintheta)) / (1-sin2theta) (costheta (1-sintheta + 1 + sintheta)) / (1-sin2theta) (2costheta) / (1-sin ^ 2theta) den pythagoranske identitet, sin ^ 2theta + cos ^ 2theta = 1. Så: cos ^ 2theta = 1-sin ^ 2theta Nu da vi ved det, kan vi skrive: (2costheta) / cos ^ 2theta 2 / costheta = 4 costheta / 2 = 1/4 costheta = 1/2 theta = cos ^ 1 (1/2) theta = pi / 3, n
Forenkle (1-cos theta + sin theta) / (1 + cos theta + sin theta)?
= sin (theta) / (1 + cos (theta)) (1-cos (theta) + sin (theta)) / (1 + cos (theta) + sin (theta)) = (1-cos (theta) + synd (theta)) * (1 + cos (theta) + sin (theta)) / (1 + cos (theta) + sin (theta)) 2 = ((1 + sin (theta) 2 (theta)) (1 + cos ^ 2 (theta) + sin ^ 2 (theta) + 2 sin (theta) +2 cos (theta) + 2 sin (theta) cos (theta)) = synd (theta)) 2-cos ^ 2 (theta)) / (2 + 2 sin (theta) +2 cos (theta) + 2 sin (theta) cos (theta)) = ((1 + sin (theta) ) ^ 2-cos ^ 2 (theta)) / (2 (1 + cos (theta)) + 2 sin (theta) (1 + cos (theta)) = (1/2) ((1 + sin (theta) ) ^ 2-cos ^ 2 (theta)) / (1 + cos (theta)) (1 + sin (theta)) = (1/2) (1 +
Vis at, (1 + cos theta + i * sin theta) ^ n + (1 + cos theta - i * sin theta) ^ n = 2 ^ (n + 1) * (cos theta / 2) ^ n * cos n * theta / 2)?
Se nedenfor. Lad 1 + costheta + isintheta = r (cosalpha + isinalpha), her r = sqrt ((1 + costheta) ^ 2 + sin ^ 2theta) = sqrt (2 + 2costheta) = sqrt (2 + 4cos ^ 2 (theta / 2 ) -2) = 2cos (theta / 2) og tanalpha = sintheta / (1 + costheta) == (2sin (theta / 2) cos (theta / 2)) / (2cos ^ 2 (theta / 2)) = tan (theta / 2) eller alfa = theta / 2 derefter 1 + costheta-isintheta = r (cos (-alpha) + isin (-alpha)) = r (cosalpha-isinalpha) og vi kan skrive (1 + costheta + isintheta) ^ n + (1 + costheta-isintheta) ^ n ved anvendelse af DE MOivre's sætning som rnn (cosnalpha + isinnalpha + cosnalpha-isinnalpha) = 2r ^ ncosna