대답:
아래를 봐주세요.
설명:
우리는, # LHS = tan20 ^ circ + tan80 ^ circ + tan140 ^ circ #
#color (흰색) (좌) = tan20 ^ circ + tan (60 ^ circ + 20 ^ circ) + tan (120 ^ circ + 20 ^ circ) #
#color (흰색) (좌) #=(tan120 ^ circ + tan20 ^ circ) / (1-tan60 ^ circtan20 ^ circ) + (tan120 ^ circ + tan20 ^ circ) /
Subst. #color (파란색) (tan60 ^ circ = sqrt3, tan120 ^ circ = -sqrt3 및 tan20 ^ circ = t #
# LHS = t + (sqrt3 + t) / (1- sqrt3t) + (- sqrt3 + t) / (1 + sqrt3t) #
(1-sqrt3t) (1 + sqrt3t) + (- sqrt3t)) / ((sqrt3t)
#color (백색) = t + (sqrt3 + 3t + t + sqrt3t ^ 2-sqrt3 + 3t + t-sqrt3t ^ 2) / (1-3t ^ 2) #
#color (흰색) (LHS) = t + (8t) / (1-3t ^ 2) #
#color (흰색) (좌) = (t-3t ^ 3 + 8t) / (1-3t ^ 2) #
#color (흰색) (좌) = (9t-3t ^ 3) / (1-3t ^ 2) #
#color (white) (LHS) = 3 (3t-t ^ 3) / (1-3t ^ 2) towhere, color (blue) (t = tan20 ^
#color (white) (LHS) = 3 (3tan20 ^ circ-tan ^ 3 ^ 20 ^ circ} / (1-3tan ^ 2 ^ 20 ^ circ) #
#color (흰색) (LHS) = 3 tan3 (20 ^ circ) toApply (2) # …에 대한 # theta = 20 ^ circ #
# LHS = 3tan60 ^ circ #
# LHS = 3sqrt3 = RHS #
노트:
# (1) tan (A + B) = (tanA + tanB) / (1-tanAtanB) #
# (2) tan3theta = (3tantheta-tan ^ 3theta) / (1-3tan ^ 2theta) #
# LHS = tan20 + tan80 + tan140 #
# = tan20 + tan80 + tan (180-40) #
# = tan20 + tan80-tan 40 #
# = tan20 + sin80 / cos80-sin40 / cos40 #
# = sin20 / cos20+ (sin80cos40-cos80sin40) / (cos80cos40) #
# = (sin 20cos 80cos 40 + sin 40cos 20) / (cos 20cos 80cos 40) #
이제이 식의 분모
# = cos 20cos 80cos 40 #
# = (4 * 2sin 20cos 20cos 40cos 80) / (8sin 20) #
# = (2 * 2sin 40cos 40cos 80) / (8sin 20) #
# = (2sin 80cos 80) / (8sin 20) #
# = (죄 160) / (8sin 20) #
# = (sin (180-20)) / (8sin 20) #
# = (sin 20) / (8sin 20) #
#=1/8#
금후
# LHS = 8 (sin 20cos 80cos 40 + sin 40cos 20) #
# = 4sin 20 * (2cos 80cos 40) + 4 * 2sin 40cos 20 #
# = 4sin20 (cos120 + cos40) +4 (sin60 + sin20) #
# = 4sin20 (-1 / 2 + cos40) +4 (sqrt3 / 2 + sin20) #
# = - 2sin 20 + 4sin 20cos 40 + 2sqrt3 + 4sin 20 #
# = 4sin 20cos 40 + 2sqrt3 + 2sin 20 #
# 2 (sin60-sin20) + 2sqrt3 + 2sin20 #
# = 2 (sqrt3 / 2-sin20) + 2sqrt3 + 2sin20 #
# = sqrt3-2sin 20 + 2sqrt3 + 2sin 20 #
# = 3sqrt3 #
anwer를 이용한 재미있는 접근법 # 3sqrt3 # 주어진.
우리는 우리가 알고있는대로 다음과 같이 LHS를 쓸 수 있습니다. # sqrt3 = tan 60 #
# LHS = tan 20 + tan 80 + tan 140 #
# = 3sqrt3 + (tan20-tan60) + (tan80-tan60) + (tan140-tan60) #
# = 3sqrt3 + (tan20-tan60) + (tan80-tan60) + (tan (180-40) -tan60) #
# = 3sqrt3 + (tan20-tan60) + (tan80-tan60) - (tan40 + tan60) #
sin (sin 40 / cos 40 + sin 60 / cos60) # (3) sin (sin 20 / cos 20-sin 60 / cos 60) + (sin 80 / cos 80-sin 60 / cos60)
# = 3sqrt3-sin (60-20) / (cos20cos60) + sin (80-60) / (cos80cos60) -sin (60 + 40) / (cos40cos60) #
# = 3sqrt3- (2sin 40) / cos 20+ (2sin 20) / cos 80- (2sin 100) / cos 40 #
# = 3sqrt3- (4sin 20cos 20) / cos 20+ (4sin 10cos 10) / sin 10- (4sin 40cos 40) / cos 40 #
# = 3sqrt3-4sin 20 + 4cos 10-4sin 40 #
# = 3sqrt3-4 (sin20 + sin40) + 4cos10 #
# = 3sqrt3-4 (2sin30cos1 0) + 4cos10 #
# = 3sqrt3-4 (2 * 1 / 2 * cos1 0) + 4cos 10 #
# = 3sqrt3-4cos 10 + 4cos 10 #
# = 3sqrt3 #
대답:
아래의 설명
설명:
# x = tan20 + tan80 + tan140 #
=# sin20 / cos20 + sin80 / cos80 + tan (180-40) #
=# (cos80 * sin20 + sin80 * cos20) / (cos80 * cos20) -tan40 #
=#sin (80 + 20) / (cos80 * cos20) -sin40 / cos40 #
=# sin100 / (cos80 * cos20) -sin40 / cos40 #
=# sin80 / (cos80 * cos20) -sin40 / cos40 #
=# (sin80 * cos40-cos80 * sin40 * cos20) / (cos80 * cos40 * cos20) #
=# (sin20 * (8sin80 * cos40-8cos80 * sin40 * cos20)) / (8cos80 * cos40 * cos20 * sin20) #
=# (sin20 * (4sin120 + 4sin40-4cos20 * (sin120-sin40))) / (4cos80 * cos40 * sin40) #
=# (sin20 * (4sin120 + 4sin40-4sin120 * cos20 + 4sin40 * cos20)) / (2cos80 * sin80) #
=# (sin20 * (4sin60 + 4sin40-4sin60 * cos20 + 4sin40 * cos20)) / (sin160) #
=# (sin20 * (4sin60 + 4sin40-2sin80-2sin40 + 2sin60 + 2sin20)) / (sin20) #
=# 6sin60 + 2sin40-2sin80 + 2sin20 #
=# 3sqrt3 + 2sin20- (2sin80-2sin40) #
=# 3sqrt3 + 2sin20-4cos60 * sin20 #
=# 3sqrt3 + 2sin20-2sin20 #
=# 3sqrt3 #
