Odgovor:
Molimo pogledajte Obrazloženje.
Obrazloženje:
Mi to znamo, # Tan3theta = (3tantheta-tan ^ 3theta) / (1-3tan ^ 2 theta) #.
#:. cot3theta = 1 / (tan3theta) = (1-3tan ^ 2 theta) / (3tantheta-tan ^ 3theta) #
#:. krevetić ((3A) / 2) = {1-3tan ^ 2 (A / 2)} / {3tan (A / 2) -tan ^ 3 (A / 2)} #.
Pustiti #tan (A / 2) = t, # imamo,
#cot (A / 2) -3cot ((3A) / 2) *, # = 1/3-t {(1-3t ^ 2) / (3t-t ^ 3)} #, # 1 / t {3 (1-3t ^ 2)} / {t (3-t ^ 2)} #, # = {(3-t ^ 2) -3 (1-3t ^ 2)} / {t (3-t ^ 2)} #, # = (8t ^ otkazivanje (2)) i / {otkazivanje (t) (3-t ^ 2)} #, # = (8t) / {(1 + t ^ 2) + 2 (1-t ^ 2)} #
# = {4 * (2t) / (1 + t ^ 2)} / {(1 + t ^ 2) / (1 + t ^ 2) + 2 * (1-t ^ 2) / (1 + t ^ 2)} #.
Imajte na umu da, # (2t) / (1 + t ^ 2) = {2tan (A / 2)} / (1 + tan ^ 2 (A / 2)) = sinA, i #
# (1-t ^ 2) / (1 + t ^ 2) = cosa #.
#rArrcot (A / 2) -3cot ((3A) / 2) = (4sinA) / (1 + 2cosA), "po želji!"
Odgovor:
Pogledajte dolje.
Obrazloženje:
# LHS = krevetić (x / 2) -3cot ((3 x) / 2) *
# = Cos (x / 2) / sin (x / 2) -3 * cos ((3 x) / 2) / sin ((3 x) / 2) *
# = (Sin ((3 x) / 2) * cos (x / 2) -3 * cos ((3 x) / 2) * sin (x / 2)) / (sin (x / 2) * sin ((3 x) / 2) *
# = (2sin ((3 x) / 2) * cos (x / 2) -3 * 2cos ((3 x) / 2) * sin (x / 2)) / (2sin (x / 2) * sin ((3 x) / 2) *
# = (Sin ((3 x) / 2 + x / 2) + sin ((3 x) / 2 x / 2) -3 * {sin ((3 x) / 2 + x / 2) -sin ((3 x) / 2 x / 2)}) / (cos ((3 x) / 2 x / 2) -cos ((3 x) / 2 + x / 2) *
# = (Sin ((4x) / 2) + sin ((2 x) / 2) -3 * {sin ((4x) / 2) -sin ((2 x) / 2)}) / (cos ((2 x) / 2) (-cos (4x) / 2) #
# = (+ Sin2x sinx-3sin2x + 3sinx) / (cosx-cos2x) #
# = (4sinx-2sin2x) / (cosx- (cos ^ 2x-sin ^ 2x)) *
# = (4sinx-4sinx * cosx) / (cosx-cos ^ 2x + sin ^ 2x) #
# = (4sinx (1-cosx)) / (cosx (1-cosx) + (1-cosx) (1 + cosx)) *
# = (4sinx (1-cosx)) / ((1-cosx) (cosx + 1 + cosx) #
# = (4sinx) / (1 + 2cosx) = RHS #
# LHS = krevetić (A / 2) -3cot ((3A) / 2) *
# = Cos (A / 2) / sin (A / 2) -cos ((3A) / 2) / sin ((3A) / 2) -2cot ((3A) / 2) *
# = (Sin ((3A) / 2) + cos (A / 2) -cos ((3A) / 2) * sin (A / 2)) / (sin (A / 2) * sin ((3A) / 2)) - 2cot ((3A) / 2) *
# = sin (A) / (sin (A / 2) * sin ((3A) / 2)) -2kot ((3A) / 2) #
# = (2sin (A / 2) cos (A / 2)) / (sin (A / 2) * sin ((3A) / 2)) -2cot ((3A) / 2) #
# = 2cos (A / 2) / sin ((3A) / 2) -2 * cos ((3A) / 2) / sin ((3 A) / 2) #
# = 2 (cos (A / 2) -cos ((3A) / 2)) / sin ((3 A) / 2) #
# = 2 (2sin (A / 2) sin (A)) / (3sin (A / 2) -4sin ^ 3 (A / 2)) #
# = (4sin (A / 2) sin (A)) / (sin (A / 2)) (3-4sin ^ 2 (A / 2)) #
# = (4sin (A)) / (3-2 (1-cosA)) #
# = (4sin (A)) / (1 + 2cosA) = RHS #
