решите уравнения 1)18y-21=3y^2-42

                                    2)(x+8)(x+7)=0

                                    3)10+8х=3ч-5

 

 

 

 

1)18y-21=3y^2-42

18y - 21 - 3y^2 +42 = 0

-3y^2 +18y +21 = 0   / : 3

-y^2 + 6y +7 =0

D = b^2 - 4ac = 6^2 - 4*(-1) * 7 = 36+28 = 64

VD = V64 = 8

x1 = (-6+8)/2*(-1) = 2/-2 = -1

x2 = (-6-8)/2*(-1) = -14/-2 = 7

2)(x+8)(x+7)=0

раскроем скобки

x^2 + 7x +8x +56 = 0

x^2 + 15x + 56 = 0

D = b^2 - 4ac = 15^2 - 4*1*56 = 225 - 224 = 1

VD = V1 = 1

x1 = (-15+1)/2 = -14/2 = -7

x2 = (-15-1)/2 = -16/2 = - 8

3)10+8х=3x-5

    10 + 8x - 3x +5 = 0

    15 + 5x = 0

    15 = -5x

     x = -3

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   10 + 8*(-3) = 3*(-3) - 5

   10 + (-24) = -9 - 5

      10 - 24 = -9 - 5

           - 14 = -14