sin(42° 30')cos(47° 30') + sin(47° 30')cos(42° 30')= sin(90°) = 1
cos(4π/9)cos(5π/18) + sin(4π/9)sin(5π/18)= cos(4π/9 + 5π/18) = cos(8π/9) = cos(π - 1/9π) = -cos(1/9π) = -cos(20°) = -√3/2
sin(13π/6) - cos(11π/6) + ctg(11π/4)= sin(π/6) - cos(π/6) + (cos(11π/4) / sin(11π/4))= 1/2 - √3/2 + (0/sin(π))= 1/2 - √3/2
sin(π/8) - sin(π/4)= sin(π/8) - sin(2π/8)= sin(π/8) - sin(π/2)= sin(π/8) - 1= sin(22.5°) - 1
cos(40°) - 20Данное выражение не имеет математического решения, так как одно из слагаемых — просто число 20, а не косинус какого-либо угла.
sin(2a), если 90 < a < 180, sin(a) = 5/13По теореме Пифагора sin^2(a) + cos^2(a) = 1cos(a) = +/- sqrt(1 - sin^2(a))cos(a) = +/- sqrt(1 - (5/13)^2)cos(a) = +/- sqrt(1 - 25/169)cos(a) = +/- sqrt(144/169)cos(a) = +/- 12/13Так как a находится во II четверти, то cos(a) = -12/13sin(2a) = 2sin(a)cos(a) = 2 (5/13) (-12/13) = -120/169
(cos^2(a/2)/sin^2(a) - 1) + (sin^2(a/2)/cos^2(a) - 1)= ((1 - sin^2(a/2))/sin^2(a)) + ((cos^2(a/2) - 1)/cos^2(a))= (cos^2(a/2)/sin^2(a)) + ((cos^2(a/2) - 1)/cos^2(a))= cot^2(a/2) + cot^2(a)
sin(3a) + 2cos(2a) - sin(a) / cos(a) + 2sin(2a) - cos(3a)= 3sin(a) - 4sin^3(a) + 2cos(2a) - sin(a) / cos(a) + 4sin(a)cos(a) - 8sin^3(a) - 3cos(a) + 4cos^3(a)= 3sin(a) - 4sin^3(a) + 2cos(2a) - sin(a) / cos(a) + 4sin(a)cos(a) - 8sin^3(a) - 3cos(a) + 4cos^3(a)
sin(42° 30')cos(47° 30') + sin(47° 30')cos(42° 30')
= sin(90°) = 1
cos(4π/9)cos(5π/18) + sin(4π/9)sin(5π/18)
= cos(4π/9 + 5π/18) = cos(8π/9) = cos(π - 1/9π) = -cos(1/9π) = -cos(20°) = -√3/2
sin(13π/6) - cos(11π/6) + ctg(11π/4)
= sin(π/6) - cos(π/6) + (cos(11π/4) / sin(11π/4))
= 1/2 - √3/2 + (0/sin(π))
= 1/2 - √3/2
sin(π/8) - sin(π/4)
= sin(π/8) - sin(2π/8)
= sin(π/8) - sin(π/2)
= sin(π/8) - 1
= sin(22.5°) - 1
cos(40°) - 20
Данное выражение не имеет математического решения, так как одно из слагаемых — просто число 20, а не косинус какого-либо угла.
sin(2a), если 90 < a < 180, sin(a) = 5/13
По теореме Пифагора sin^2(a) + cos^2(a) = 1
cos(a) = +/- sqrt(1 - sin^2(a))
cos(a) = +/- sqrt(1 - (5/13)^2)
cos(a) = +/- sqrt(1 - 25/169)
cos(a) = +/- sqrt(144/169)
cos(a) = +/- 12/13
Так как a находится во II четверти, то cos(a) = -12/13
sin(2a) = 2sin(a)cos(a) = 2 (5/13) (-12/13) = -120/169
(cos^2(a/2)/sin^2(a) - 1) + (sin^2(a/2)/cos^2(a) - 1)
= ((1 - sin^2(a/2))/sin^2(a)) + ((cos^2(a/2) - 1)/cos^2(a))
= (cos^2(a/2)/sin^2(a)) + ((cos^2(a/2) - 1)/cos^2(a))
= cot^2(a/2) + cot^2(a)
sin(3a) + 2cos(2a) - sin(a) / cos(a) + 2sin(2a) - cos(3a)
= 3sin(a) - 4sin^3(a) + 2cos(2a) - sin(a) / cos(a) + 4sin(a)cos(a) - 8sin^3(a) - 3cos(a) + 4cos^3(a)
= 3sin(a) - 4sin^3(a) + 2cos(2a) - sin(a) / cos(a) + 4sin(a)cos(a) - 8sin^3(a) - 3cos(a) + 4cos^3(a)