°°°°ДАЮ 15 БАЛОВ 8 КЛАСС°°°°

Question

°°°°ДАЮ 15 БАЛОВ 8 КЛАСС°°°°

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Answer 1

1) (x + 5/6)(x - 7) = 0
    x² + 5/6 x - 7x - 35/6 = 0
    x² - 37/6 x - 35/6 = 0
   6x² - 37x - 35 = 0                        D = b²-4ac = 1369+840 = 2209 = 47²

     x₁ = (-b+√D)/2a = (37+47)/12 = 7
     x₂ = (-b -√D)/2a = (37-47)/12 = -10/12 = -5/6            

2). (x - 0,9)(x + 11) = 0
      x² - 0,9x + 11x - 9,9 = 0
      x² + 10,1x - 9,9 = 0
   10x² + 101 - 99 = 0         D = b²-4ac = 10201+3960 = 14161 = 119²

    x₁ = (-b+√D)/2a = (-101+119)/20 = 18/20 = 0,9
    x₂ = (-b -√D)/2a = (-101-119)/20 = -220/20 = -11

3). (x + 3/4)(x - 1/3) = 0
      x² + 3/4 x - 1/3 x - 1/4 = 0
      x² + 5/12 x - 1/4 = 0
    12x² + 5x - 3 = 0        D = b²-4ac = 25+144 = 169 = 13²         

     x₁ = (-b+√D)/2a = (-5+13)/24 = 1/3
     x₂ = (-b -√D)/2a = (-5-13)/24 = -18/24 = -3/4

4). (x + 0,8)(x + 1/5) = 0
      x² + 0,8x + 0,2x + 0,16 = 0
      x² + x + 0,16 = 0
    25x² + 25x + 4 = 0          D = b²-4ac = 625-400 = 225 = 15²

    x₁ = (-b+√D)/2a = (-25+15)/50 = -1/5
    x₂ = (-b -√D)/2a = (-25-15)/50 = - 0,8              

Answer 2

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