Вот еще одно (3 9\13 +y)-4 9\13=1 7\13

(3 9/13+у)-4 9/13=1 7/13

у=1 7/13+4 9/13-3 9/13

у=2 7/13

(3 9\13+у)-4 9\13=1 7\13

3 9\13+у=1   7\13+ 4   9\13

3   9\13+у= 6   3\13

у= 6   3\13-3   9\13

у=2   7\13

(3   9\13+2   7\13)-   4   9\13=1   7\13

8х²+3х=0 x(8x + 3) = 0 x₁ = 0 8x + 3 = 0 8x = - 3 x₂ = - 3/8 2)  3х²  -  8  =  0 3x² = 8 x² = 8/3 a)  x = -  √(8/3) x₁ = (- 2/3)√6 b)  x =   √(8/3) x₂ = (  2/3)√6 3)  5u²  -  6u  =  0 u(5u - 6) = 0 u₁ = 0 5u - 6 = 0 u₂ = 6/5 u₂ = 1(1/5) 4)   2a  -  4a²  =  0 2a(1 - 2a) = 0 2a = 0 a₁ = 0 1 - 2a = 0 a₂ = 1/2 5)  1  -  16y²  =  0 16y² = 1 y² = 1/16 y₁ = - 1/4 y₂ = 1/4 6)   2x²  -  4  =  0 2x² = 4 x² = 2 x₁ = -  √2 x₂ =  √2

1)   cosa = - 12/13  a)   sina =  √[1 - (144/169)] =  √(25/169) = 5/13 sina = -  √[1 - (144/169)] = -  √(25/169) = -  5/13 б   ) tga = sina/cosa tgx  =(5/13) : (- 12/13) = - 5/12 tgx = (-5/13) : (-12/13) = 5/12 в)   ctgx = 1/tgx ctgx = - 12/5 ctgx = 12/5 2) вычислить: ctg (-210градусов) +cos(-900 градусов)+ sin(-15пи/4) решение - ctg(180° + 30⁺) + cos(2*360° + 180°) - sin(  4π-  π/4) = =  -  √3 + cos180° - sin(π/4) = -  √3 - 1 -  √2/2(2√3 -  √2 - 2)/2 3) : ( 2sin² a )/( 1-cos a ) - 2cos a =   =  [2sin² a - 2*(cosa - cos²a)] / (1 - cosa) =    =    [2sin² a - 2cosa + 2cos²a)] / (1 - cosa) =    2*(1 - cosa) /(1 - cosa) = 2  4) преобразовать в произведение: cos40° - cos20г° = 2*[sin(40° + 20°)/2]  *[sin(40° - 20°)/2] =  = 2*sin30° * sin10° = 2*(1/2)*sin10° = sin10° 5) : cos ( 7пи/5+ a) cos (2пи/5 + a) + sin(7пи/5 + a) sin ( 2пи/5 + a) =  = cos(7π/5 + a - 2π/5 - a) = cos(π) = - 1